1
Q
How does temperature affect microbial growth?
A
Follows a bell curve
2
Q
What does the peak of the temperature bell curve represent?
A
Optimum growth temperature
3
Q
Do all organisms have the same optimum growth temperature?
A
No, each organism has its own optimum
4
Q
Do most microorganisms grow best at temperatures humans favor?
A
Yes
5
Q
What makes some bacteria unique compared to most eukaryotes regarding temperature?
A
They can grow at extreme temperatures that hinder survival of almost all eukaryotic organisms
6
Q
Do most bacteria grow across a wide or limited temperature range?
A
A limited temperature range
7
Q
What does ‘phile’ mean?
A
Loving
8
Q
WHat does ‘psychro’ mean?
A
Cold
9
Q
What are psychrophiles
A
Cold-loving organisms
10
Q
At what temperatures can true psychrophiles grow?
A
0°C or below
11
Q
What is the optimum growth temperature for true psychrophiles?
A
~15°C
12
Q
Can true psychrophiles grow at room temperature (20–25°C)?
A
No
13
Q
Will true psychrophiles survive at room temperature?
A
No
14
Q
Where are true psychrophiles found?
A
Polar regions
15
Q
What are microorganisms that prefer cold temperatures called?
A
Psychrophiles (cold-loving microbes)
16
Q
What are microorganisms that prefer moderate temperatures called?
A
Mesophiles (moderate-temperature-loving microbes)
17
Q
What are microorganisms that prefer high temperatures called?
A
Thermophiles (heat-loving microbes)
18
Q
How do bacteria grow at the high and low extremes of their temperature range?
A
Poorly
19
Q
Approximately how wide is a bacterium’s typical temperature growth range?
A
About 30°C
20
Q
What is the minimum growth temperature?
A
The lowest temperature at which the species will grow
21
Q
What is the optimum growth temperature?
A
The temperature at which the species grows best
22
Q
What is the maximum growth temperature?
A
The highest temperature at which growth is possible
23
Q
Where is the optimum growth temperature usually located on a temperature growth curve?
A
Near the top of the temperature range
24
Q
What happens to growth rate above the optimum growth temperature?
A
It drops off rapidly
25
Why does growth drop rapidly above the optimum temperature?
High temperature inactivates necessary enzymatic systems of the cell
26
How are psychrotrophs described?
Very flexible / facilitative cold-loving organisms
27
Can psychrotrophs grow at 0°C or below?
Yes
28
What is the optimum temperature range for psychrotrophs?
20–30°C
29
Can psychrotrophs grow at 40°C?
No
30
Why are psychrotrophs clinically important?
They can cause disease
31
Where can psychrotrophs grow?
Rooms and food
32
What problem do psychrotrophs commonly cause?
Food spoilage
33
Give examples of organisms associated with psychrotrophs.
Molds
34
What foods commonly show psychrotroph growth?
Protein-rich foods
35
What are visible signs of psychrotroph growth?
Slimy layer on foods
36
Give examples of food spoilage caused by psychrotrophs.
Slime on chicken, mold on bread
37
How do psychrotrophs cause disease (as written)?
From odor / food spoilage
38
Psychrophiles were originally defined as organisms capable of growing at what temperature?
0°C
39
True psychrophiles can grow at what minimum temperature?
0°C
40
What is the optimum growth temperature of true psychrophiles?
About 15°C
41
Can true psychrophiles grow at room temperature (25°C)?
No
42
Where are true psychrophiles most commonly found?
Ocean depths and polar regions
43
Do true psychrophiles commonly cause food preservation problems?
No
44
Psychrotrophs can grow at what minimum temperature?
0°C
45
What is the optimum growth temperature range of psychrotrophs?
20–30°C
46
Above what temperature do psychrotrophs generally not grow?
About 40°C
47
Are psychrotrophs more or less common than true psychrophiles?
More common
48
Why are psychrotrophs important in food microbiology?
They commonly cause low-temperature food spoilage
49
Why are psychrotrophs able to spoil refrigerated food?
They grow fairly well at refrigerator temperatures
50
Which term do food microbiologists prefer for these spoilage organisms?
Psychrotrophs
51
What is the most common method of preserving household food supplies?
Refrigeration
52
Refrigeration works based on what principle?
Microbial reproductive rates decrease at low temperatures
53
Do microbes usually survive subfreezing temperatures?
Yes
54
What often happens to microbes at subfreezing temperatures?
They may become dormant (alive, but not active)
- cold temps preserve microbes rather than killing them
55
What happens to microbial populations over time at low temperatures?
They gradually decline in number
56
Do all microbial species decline at the same rate during refrigeration?
No
57
Do psychrotrophs grow well at low temperatures compared to other organisms?
Yes
58
Given enough time, what can psychrotrophs do to refrigerated food?
Slowly degrade it
59
What are common signs of spoilage caused by psychrotrophs?
Mold mycelium, bacterial slime, off-tastes, off-colors
60
What effect does a properly set refrigerator have on spoilage organisms?
Greatly slows their growth
61
What effect does refrigeration have on pathogenic bacteria?
Prevents growth of all but a few
62
Why should large amounts of warm food be divided before refrigeration?
Large quantities cool too slowly
63
What temperature range do mesophiles grow in?
25–40°C
64
What is the optimum temperature for mesophiles?
37°C
65
Can mesophiles grow above 45–50°C?
No
66
What important group of microbes are mesophiles?
Pathogens
67
What is the basic principle of refrigeration?
Low temperatures decrease microbial reproduction rates.
68
What is the effect of heating foods to high temperatures?
Heating foods to high temperatures destroys most microbes.
69
Are there exceptions to typical temperature responses of bacteria?
Yes, some bacteria grow well at high temperatures that would kill most bacteria, and a few can grow at temperatures well below freezing.
70
What happens to bacterial growth at refrigerator temperatures?
May allow slow growth of spoilage bacteria; very few pathogens.
71
What happens to bacterial growth below freezing?
No significant growth below freezing.
72
What occurs in the “danger zone” temperature range?
Rapid growth of bacteria; some may produce toxins.
73
What happens at temperatures just above refrigeration but below the danger zone?
Many bacteria survive; some may grow.
74
What happens at very high temperatures (upper range on thermometer)?
Temperatures in this range destroy most microbes, although lower temperatures take more time.
75
What is the optimum growth temperature range for mesophiles?
25–40°C.
76
What type of microbe is the most common?
Mesophiles.
77
What is the optimum temperature for organisms adapted to live in animal bodies?
Close to the temperature of their hosts.
78
What is the optimum growth temperature for many pathogenic bacteria?
About 37°C.
79
At what temperature are incubators usually set for clinical cultures?
About 37°C.
80
What types of organisms do mesophiles include?
Most common spoilage and disease organisms.
81
Can thermophiles grow below 45°C?
No
82
What is the optimum growth temperature for thermophiles?
65–70°C
83
What is the highest temperature thermophiles can grow at?
Up to 80°C
84
How hot can hyperthermophiles grow?
Up to 110°C
85
Are hyperthermophiles a health concern?
No
86
Are hyperthermophiles pathogenic (disease causing)
No
87
Do hyperthermophiles cause disease?
No
88
thermophiles
Microorganisms capable of growth at high temperatures.
89
typical optimum growth temperature range for many thermophiles
50–60°C.
90
Where can thermophilic temperatures naturally occur?
Sunlit soil and thermal waters such as hot springs.
91
Below what temperature can many thermophiles NOT grow?
Below about 45°C.
92
What is unusual about endospores formed by thermophilic bacteria?
They are unusually heat resistant.
93
What food processing treatment may thermophilic endospores survive?
The usual heat treatment given canned goods.
94
How can elevated storage temperatures affect thermophilic endospores in food?
They may germinate and grow, spoiling the food.
95
Are thermophilic bacteria considered a public health problem?
No.
96
In what setting are thermophiles especially important?
Organic compost piles.
97
What temperatures can compost piles reach due to thermophiles?
50–60°C.
98
What group of microbes includes many hyperthermophiles?
Archaea.
99
What is the optimum growth temperature of hyperthermophiles?
80°C or higher.
100
What are hyperthermophiles sometimes also called?
Extreme thermophiles.
101
Where do most hyperthermophiles live?
Hot springs associated with volcanic activity.
102
What element is usually important in the metabolic activity of hyperthermophiles?
Sulfur.
103
Does microbial growth depend on environmental pH?
A: Yes
yes
104
What does pH refer to?
The acidity or alkalinity of a solution.
105
What pH range do most bacteria grow best in?
Near neutrality, between pH 6.5 and 7.5.
106
Below approximately what pH do very few bacteria grow?
Below about pH 4.
107
Why are foods like sauerkraut, pickles, and many cheeses preserved from spoilage?
Acids produced by bacterial fermentation inhibit bacterial growth.
108
How does acidity affect microbial growth?
Acidic conditions inhibit the growth of most bacteria.
109
Is alkalinity commonly used to preserve foods?
No, alkalinity inhibits microbial growth but is rarely used to preserve foods.
110
What are acidophiles?
Bacteria that are remarkably tolerant of acidity.
111
What is an example of extremely acid-tolerant bacteria mentioned?
A chemoautotrophic bacterium found in drainage water from coal mines.
112
What metabolic process allows Acidithiobacillus ferrooxidans bacterium to survive extreme acidity?
Oxidizing sulfur to form sulfuric acid.
113
To what pH can H.Pylori bacterium survive?
pH 1.
114
How does the pH growth range of molds and yeasts compare to bacteria?
They grow over a greater pH range than bacteria.
115
What is the usual optimum pH range for molds and yeasts?
About pH 5 to 6.
116
Is the optimum pH of molds and yeasts higher or lower than bacteria?
Lower than bacteria.
117
Why does bacterial growth eventually interfere with itself in laboratory cultures?
Bacteria produce acids that interfere with their own growth.
118
What is added to growth media to neutralize acids and maintain proper pH?
Chemical buffers.
119
What components of some media act as buffers?
Peptides and amino acids.
120
What type of salts are commonly included in media for buffering?
Phosphate salts.
121
Why are phosphate salts advantageous as buffers?
They buffer in the pH growth range of most bacteria and are nontoxic.
122
Besides buffering, what additional benefit do phosphate salts provide?
They provide phosphorus, an essential nutrient.
123
What affects microbial growth related to osmotic pressure?
Solute concentration
124
How do microorganisms obtain almost all of their nutrients?
In solution from the surrounding water.
125
Why do microorganisms require water for growth?
Because nutrients are obtained in solution from surrounding water.
126
What percentage of a microbial cell’s composition is water?
Approximately 80–90%.
127
What effect do high osmotic pressures have on microbial cells?
They remove necessary water from the cell.
128
What happens when a microbial cell is placed in a solution with a higher solute concentration than the cell?
Cellular water passes out through the plasma membrane toward the higher solute concentration.
129
What term describes an environment with a higher solute concentration than the cell?
Hypertonic to the cell
Hypertonic means more solute outside the cell than inside the cell
130
What is plasmolysis?
Shrinkage of the cell’s cytoplasm due to osmotic loss of water.
131
What causes plasmolysis?
Osmotic loss of water when the cell is in a hypertonic environment.
132
Through what structure does water leave the cell during plasmolysis?
The plasma membrane.
133
Why does high osmotic pressure inhibit microbial growth?
It removes water necessary for cellular processes.
134
How do microorganisms obtain most of their nutrients?
In solution from the surrounding water.
135
What percentage of a microbial cell’s composition is water?
About 80–90%.
136
Why is water required for microbial growth?
Microorganisms obtain nutrients dissolved in water.
137
What is the effect of high osmotic pressure on a microbial cell?
It removes necessary water from the cell.
138
What does it mean when an environment is hypertonic to a cell?
The solute concentration outside the cell is higher than inside the cell.
139
What happens to cellular water in a hypertonic environment?
Water passes out of the cell through the plasma membrane.
140
What is plasmolysis?
Shrinkage of the cell’s cytoplasm due to osmotic loss of water.
141
How does plasmolysis affect microbial growth?
Growth of the cell is inhibited.
142
How can osmotic pressure be used to preserve foods?
Adding salts or other solutes increases osmotic pressure, drawing water out of microbial cells and preventing growth.
143
Name three foods preserved largely by osmotic pressure.
Salted fish, honey, and sweetened condensed milk.
144
What causes water to be drawn out of microbial cells in preserved foods?
High salt or sugar concentrations.
145
What happens if osmotic pressure is unusually low (hypotonic environment)?
Water tends to enter the cell.
146
What determines a microbe’s oxygen category?
Chemical use of oxygen
147
Why do we commonly think of molecular oxygen (O₂) as necessary for life?
Many current forms of life have metabolic systems that require oxygen for aerobic respiration.
148
Why is molecular oxygen (O₂) described as a poisonous gas?
Oxygen is potentially toxic despite being used by many organisms.
149
Why might life not have arisen if oxygen had been present early in Earth’s history?
Oxygen is toxic, and early life likely could not tolerate it.
150
What metabolic process requires oxygen in many modern organisms?
Aerobic respiration.
151
What happens to hydrogen atoms stripped from organic compounds during aerobic respiration?
They combine with oxygen to form water.
152
What are the benefits of hydrogen combining with oxygen to form water?
It yields a great deal of energy while neutralizing a potentially toxic gas.
153
Which microbes extract more energy from nutrients: aerobes or anaerobes?
Aerobes.
154
What term describes microbes that use molecular oxygen?
Aerobes.
155
What term describes microbes that do not use oxygen?
Anaerobes.
156
What are organisms that require oxygen to live called?
Obligate aerobes.
157
What does “obligate” mean?
Absolute
158
Do obligate aerobes require oxygen?
Yes, they absolutely require oxygen for growth
159
What pathways do obligate aerobes use?
Glycolysis + full aerobic pathway
160
How much ATP do obligate aerobes produce from glucose?
38 ATP
161
What electron acceptor do obligate aerobes use?
Oxygen
162
How do obligate aerobes grow in culture (as per diagram)?
Show really good growth (“absolute arrows”)
163
Why is molecular oxygen (O₂) considered poisonous, despite being essential for many organisms?
Because it is highly reactive and forms toxic oxygen derivatives that can damage cellular components.
164
What happens to hydrogen atoms stripped from organic compounds during aerobic respiration?
They combine with oxygen to form water.
165
Why does aerobic respiration yield a large amount of energy?
Because combining hydrogen with oxygen releases a great deal of energy.
166
Which microbes extract more energy from nutrients: aerobes or anaerobes?
Aerobes.
167
What are obligate aerobes?
Organisms that require oxygen to live.
168
Why are obligate aerobes at a disadvantage in many environments?
Because oxygen is poorly soluble in water.
169
What are facultative anaerobes?
Organisms that use oxygen when it is present but can grow without oxygen using fermentation or anaerobic respiration.
170
What happens to energy production in facultative anaerobes when oxygen is absent?
Their efficiency in producing energy decreases.
171
Give an example of a facultative anaerobe mentioned in the text.
Escherichia coli in the human intestinal tract.
172
How do yeasts produce energy when growing anaerobically?
By fermentation.
173
How do many bacteria produce energy when growing anaerobically?
By anaerobic respiration.
174
What are anaerobes?
Bacteria that are unable to use molecular oxygen for energy-yielding reactions.
175
What effect does oxygen have on most anaerobes?
It is harmful to them.
176
How does oxygen affect obligate anaerobes?
Oxygen is harmful
177
Do obligate anaerobes ever use oxygen for energy?
No
178
What pathways do obligate anaerobes use?
Glycolysis + fermentation
179
Is ATP production fixed in obligate anaerobes?
No, it is variable
180
What does growth depend on in obligate anaerobes?
How much energy they have
181
Give an example of an obligate anaerobe.
Clostridium tetani
182
How do obligate anaerobes grow (as written)?
At various rates
183
Why is molecular oxygen (O₂) considered poisonous, despite being essential for many organisms?
Because it is highly reactive and forms toxic oxygen derivatives that can damage cellular components.
184
Why might life not have arisen if oxygen had been present early in Earth’s history?
Because oxygen is toxic, and early life likely could not tolerate its reactive by-products.
185
Why do many modern organisms still require oxygen?
Because their metabolic systems use oxygen for aerobic respiration to produce large amounts of energy.
186
What happens to hydrogen atoms stripped from organic compounds during aerobic respiration?
They combine with oxygen to form water.
187
Why does aerobic respiration yield a large amount of energy?
Because combining hydrogen with oxygen releases a great deal of energy.
188
Which microbes extract more energy from nutrients: aerobes or anaerobes?
Aerobes.
189
What are obligate aerobes?
Organisms that require oxygen to live.
190
Why are obligate aerobes at a disadvantage in many environments?
Because oxygen is poorly soluble in water.
191
What are facultative anaerobes?
Organisms that use oxygen when it is present but can grow without oxygen using fermentation or anaerobic respiration.
192
What happens to energy production in facultative anaerobes when oxygen is absent?
Their efficiency in producing energy decreases.
193
Give an example of a facultative anaerobe mentioned in the text.
Escherichia coli in the human intestinal tract.
194
How do yeasts produce energy when growing anaerobically?
By fermentation.
195
How do many bacteria produce energy when growing anaerobically?
By anaerobic respiration.
196
What are anaerobes?
Bacteria that are unable to use molecular oxygen for energy-yielding reactions.
197
What effect does oxygen have on most anaerobes?
It is harmful to them.
198
Which genus is a familiar example of anaerobes that cause tetanus and botulism?
Clostridium.
199
How does Clostridium obtain energy?
By anaerobic respiration.
200
What is singlet oxygen (¹O₂)?
Normal molecular oxygen boosted into a higher-energy state that is extremely reactive.
Normal oxygen that becomes extremely reactive (energized)
201
What are superoxide radicals (O₂⁻)
Toxic free radicals formed in small amounts during normal aerobic respiration.
202
Why are superoxide radicals dangerous to cells?
Because their instability causes them to steal electrons from other molecules, creating damaging chain reactions.
203
What enzyme must organisms growing in oxygen produce to neutralize superoxide radicals?
Superoxide dismutase (SOD).
204
Which organisms produce superoxide dismutase (SOD)?
Aerobes, facultative anaerobes growing aerobically, and aerotolerant anaerobes.
205
Why is hydrogen peroxide (H₂O₂) toxic?
Because it contains the peroxide anion (O₂²⁻).
206
What is the role of hydrogen peroxide in antimicrobial agents?
It is the active ingredient in hydrogen peroxide and benzoyl peroxide.
207
Why must microbes neutralize hydrogen peroxide?
Because it is produced during normal aerobic respiration and is toxic.
208
What enzyme converts hydrogen peroxide into water and oxygen?
Catalase.
209
How is catalase easily detected in the lab?
By the release of oxygen bubbles when hydrogen peroxide is added to bacterial cells.
210
Why does hydrogen peroxide bubble on human wounds?
Because human tissues contain catalase.
211
What enzyme breaks down hydrogen peroxide without producing oxygen?
Peroxidase.
212
What are microaerophiles?
Aerobic bacteria that require oxygen but only grow at oxygen concentrations lower than those in air.
213
Do microaerophiles require oxygen?
Yes, they are aerobic and require oxygen.
214
Why can’t microaerophiles grow in normal atmospheric oxygen levels?
They are sensitive to oxygen-rich conditions.
215
Where do microaerophiles grow in a test tube of solid nutrient medium?
At a depth where small amounts of oxygen have diffused into the medium.
216
Where do microaerophiles NOT grow in a test tube?
Not near the oxygen-rich surface and not below the narrow zone of adequate oxygen.
217
What causes the limited oxygen tolerance of microaerophiles?
Sensitivity to superoxide radicals and peroxides.
218
What happens to microaerophiles under oxygen-rich conditions?
They produce superoxide radicals and peroxides in lethal concentrations.
219
What dies facultative mean in terms of oxygen use?
Can switch depending on oxygen availability
220
What is the final electron acceptor
Oxygen
221
how much ATP is produced
38 ATP
222
metabolic mode used when oxygen is NOT available
Anaerobic mode
223
how does ATP production change
Produces less ATP
224
what happens to growth
Growth slows but does not die
225
example of a facultative anaerobe
Escherichia coli (E. coli)
226
Can aerotolerant anaerobes tolerate oxygen
Yes
227
Do aerotolerant anaerobes use oxygen
No, they choose not to use oxygen
228
type of metabolism do aerotolerant anaerobes use
Fermentation
229
what are aerotolerant anaerobes also called
Obligate fermenters
230
what pathway do they use
Glycolysis only
231
how much ATP do aerotolerant anaerobes produce
2 ATP
232
example of an aerotolerant anaerobe
Lactobacillus species
233
what product do Lactobacillus species produce
Lactic acid
234
Do microaerophiles use oxygen
Yes
235
how much oxygen do microaerophiles require
Small amounts only
236
key difference for microaerophiles
They require low oxygen levels
237
metabolic pathways do microaerophiles use
Glycolysis + Krebs cycle
238
how does their energy yield compare
Similar to 38 ATP
239
how do microaerophiles grow
Very well, but only at low oxygen levels
240
where do microaerophiles grow in a tube
Middle (not high, not low)
241
example of a microaerophile that causes ulcers
Helicobacter pylori
242
example of a microaerophile that causes gastroenteritis
Campylobacter jejuni
243
where is Campylobacter jejuni commonly found
Undercooked chicken
244
what are bacteria called that cannot grow in the presence of oxygen
Anaerobes
245
what are bacteria that grow only without oxygen sometimes called
Anaerobes or fermenters
246
How does biofilm formation begin?
When one organism attaches to a surface
247
What happens after the first organism attaches?
Other cells sense that something is there
248
What do additional cells do once they sense attachment?
Come and form a bundle on top of the initial organism
249
How does the biofilm grow over time?
Cells build up on the initial organism
250
What process do cells use to communicate during biofilm formation?
Quorum sensing
251
What did the professor mean by “quantum sensing”?
Quorum sensing (cell-to-cell sensing)
252
What does quorum sensing allow organisms in a biofilm to do?
Change their behavior
253
How does quorum sensing affect pathogenicity?
Makes organisms more dangerous
254
Why are biofilms clinically important?
Cells communicate, change behavior, and become more dangerous
255
Why are biofilms considered the most dangerous form of infection?
They are persistent and continuously infect the patient
256
What happens if a biofilm is present in a patient?
It will keep infecting the patient
257
How do organisms exist within a biofilm?
They form a community
258
Do organisms in biofilms communicate with each other?
Yes
259
What does communication within a biofilm allow organisms to do?
Coordinate behavior
260
Can biofilms move from one location to another?
Yes
261
How do biofilms spread to new sites?
They can detach from one surface, travel, and form another biofilm
262
Why are biofilms especially hard to control?
They persist, communicate, coordinate behavior, and can spread to new surfaces
263
How do microorganisms usually live in nature compared to lab plates?
They usually live in communities called biofilms, not isolated single-species colonies.
264
What is a biofilm?
A thin, slimy layer encasing bacteria that adheres to a surface.
265
Why were biofilms not well appreciated historically?
Their three-dimensional structure was not visible until the development of confocal microscopy.
266
Why are biofilms considered biological systems rather than slime layers?
Because the bacteria are organized into a coordinated, functional community.
267
Where are biofilms commonly found?
On surfaces, such as: Rocks in ponds, Human teeth (plaque), Catheters
268
Can a biofilm contain more than one species?
Yes — it can be single-species or a diverse group of microorganisms.
269
What large environmental example of biofilms is mentioned?
Plastic pieces (~5 mm) floating in oceans that host biofilms with hundreds of bacterial and algal species.
270
Do different plastics host different biofilm communities?
Yes — different species are found on different types of plastic (e.g., polypropylene vs polyethylene).
271
What forms can biofilms take in fast-flowing environments?
Filamentous streamers
272
How do bacteria benefit from living in a biofilm?
They: Share nutrients, Are protected from desiccation, Are sheltered from antibiotics, Are protected from the immune system
273
What is the most important hospital example of biofilm formation?
Catheters
274
What other hospital equipment commonly develops biofilms?
IV tubes and medical devices
275
What happens when organisms attach to a catheter?
They form a biofilm
276
Why does a biofilm on a catheter create an infection cycle?
Organisms grow on the catheter, leave it, and infect other sites
277
What can biofilm organisms do after growing on a catheter?
Leave the catheter and enter another site in the patient
278
What is the result of this process?
Serious patient complications
279
What are hospital-acquired infections (HAIs)?
Infections that occur in a hospital setting
280
What is a major cause of hospital-acquired infections?
Biofilms
281
What are hospital-acquired infections also called?
Nosocomial infections, Healthcare-associated infections
282
What does “nosocomial infection” mean?
An infection that started in the hospital
283
Did a nosocomial infection come from the patient originally?
No
284
Give examples of nosocomial infections.
Catheter infections and IV tube infections
285
Why are nosocomial infections clinically important?
They are real-life infections commonly seen in healthcare
286
What can happen to medical catheters over time?
They can become full of bacteria
287
What happens if bacterial colonies form on a catheter?
They can leave the catheter and enter the patient
288
What can this lead to clinically?
Major problems for the patient
289
Why are catheter biofilms dangerous in hospitals?
They act as reservoirs that continuously seed infections in patients
290
Why are biofilms important in human health?
Microbes in biofilms are ~1000× more resistant to microbicides, making infections difficult to treat.
291
What percentage of human bacterial infections involve biofilms (CDC estimate)?
~70% of human bacterial infections.
292
What healthcare devices are commonly associated with biofilm formation?
Medical catheters and other indwelling medical devices (e.g., mechanical heart valves).
293
Which organisms can form biofilms besides bacteria?
Fungi, such as Candida.
294
Give clinical examples of biofilm-associated infections.
Catheter-associated infections, Dental caries (plaque), Contact lens–associated infections, Pseudomonas infections.
295
Why is prevention of biofilms critical in healthcare settings?
Biofilms increase resistance to antimicrobials and contribute to persistent, device-associated infections.
296
One strategy to prevent biofilm formation on medical devices?
Incorporating antimicrobials into surfaces where biofilms might form.
297
Why is microbiology shifting focus from planktonic to biofilm growth?
Microorganisms primarily live in biofilms in nature, which is more relevant to industrial and medical research.
298
How is biofilm formation beneficial to a pathogen?
It protects the pathogen from antimicrobials and the immune system.
299
What is a culture medium?
A nutrient material prepared to grow microorganisms in the lab.
300
What is an inoculum?
Microbes introduced into a culture medium to start growth.
301
What is a culture?
Microbes that grow and multiply in or on a culture medium.
302
What conditions must a culture medium provide?
Correct nutrients, moisture, proper pH, suitable oxygen level, sterility, and proper temperature.
303
Why must culture media be sterile initially?
To ensure only the added microbes grow.
304
What is agar?
A polysaccharide from marine algae used to solidify culture media.
305
Why is agar ideal for microbiology?
Few microbes degrade it, and it stays solid at incubation temperatures.
306
At what temperatures does agar melt and solidify?
Melts at ~100°C; solidifies at ~40°C.
307
What is an agar slant?
Agar solidified in a tilted test tube to increase surface area.
308
What is an agar deep?
Agar solidified in an upright test tube.
309
What are Petri plates?
Shallow dishes containing solid agar used to grow cultures.
310
Why are tubes commonly used to culture organisms?
They are the easiest way to culture organisms
311
Why are tubes suitable for culturing microbes?
They are sterile, come from a manufacturer, and have a cap
312
What is a broth medium?
A liquid medium
313
What is another name for liquid medium?
Broth medium
314
Broth media are similar to whose early microbiology work?
Pasteur
315
What is the basic procedure when using broth medium?
Add the organism into the broth
316
What else can be added to the broth medium?
Patient specimen
317
How is a throat swab used with broth medium?
Dip the swab into the broth
318
What happens after organisms are added to broth?
Organisms begin to proliferate
319
Do broth cultures show colony appearance?
No
320
What is the physical appearance of broth cultures?
Watery
321
Are broth cultures useful for diagnosis on their own?
No, not useful alone
322
Why are broth cultures often followed by other culture methods?
Because they do not show colony morphology and cannot be used alone for diagnosis
323
What is a complex medium?
A medium with unknown exact composition; nutrients mainly from proteins.
324
What provides vitamins and growth factors in complex media?
Meat extracts or yeast extracts.
325
What vitamins are yeast extracts especially rich in?
B vitamins.
326
What is nutrient broth?
A complex medium in liquid form.
327
What is nutrient agar?
Nutrient broth + agar.
328
Is agar a nutrient?
No — agar is only a solidifying agent.
329
Why do anaerobes require special media?
Oxygen can kill them.
330
What are reducing media?
Media that remove dissolved oxygen.
331
What chemical is commonly used in reducing media?
Sodium thioglycolate.
332
How is oxygen removed from reducing media before use?
Media are heated briefly to drive off absorbed oxygen.
333
How can anaerobes be grown on Petri plates?
Using sealed jars/boxes that chemically remove oxygen.
334
Why do we move from broth to Petri dishes?
To see colonies
335
How do you get organisms onto a Petri dish?
Transfer from broth to Petri dish
336
What is added to broth to make a Petri dish medium?
Agar
337
How does a Petri dish medium differ from broth?
It is solid instead of liquid
338
What is the key purpose of using Petri dishes in microbiology?
To observe colony growth and appearance
339
What is agar?
A complex polysaccharide
340
What is agar often compared to by analogy?
Gelatin used in painting (but much more powerful)
341
What is the main function of agar in microbiology?
Solidifying agent
342
What does agar do to liquid broth?
Makes it solid
343
What does agar provide for microbial growth?
A solid background
344
What does a solid background allow you to do?
See colonies and obtain pure cultures
345
Can organisms use agar as a food source?
No
346
Can organisms dissolve agar?
No
347
Why is it good that bacteria cannot break down agar?
The solid medium stays intact
348
At what temperature does agar melt?
~100°C
349
Why is this melting temperature useful?
It is near sterilization temperature
350
What must be done after agar melts?
Cool it down before pouring
351
How is agar cooled before pouring?
In a water bath
352
To what temperature is agar cooled before pouring?
~45°C
353
Why is 45°C ideal for pouring agar?
Cool enough to pour but still liquid
354
Where is molten agar poured?
Plates / Petri dishes
355
What happens to gelatin at room temperature?
Melts
356
What happens to agar at room temperature and 37°C?
Becomes solid and remains solid
357
Why is 37°C important?
Perfect temperature for bacterial growth
358
What do agar plates allow you to visualize?
Colonies
359
What do agar plates allow you to isolate?
Individual organisms
360
Why are agar plates best for pure cultures?
They allow isolation and clear colony formation
361
Are nutrient broth cultures good for diagnosis?
No
362
Why are agar plates better for diagnosis?
They show colonies clearly
363
How are agar plates used in diagnosis?
To identify organisms and infections
364
What is the best way to grow organisms for identification?
Agar plates
365
What are broth cultures mainly used for?
Growth only, not diagnosis
366
What are selective media?
Media that suppress unwanted microbes and allow desired ones to grow.
367
What are differential media?
Media that distinguish organisms based on visible reactions.
368
facultative
Can switch metabolic pathways depending on oxygen availability
369
final electron acceptor
Oxygen
370
how much ATP is produced
38 ATP
371
metabolic mode used when oxygen is not available
Anaerobic mode
372
how does ATP production change when oxygen is not available
Produces less ATP
373
what happens to growth rate when oxygen is not available
Growth slows but the organism does not die
374
example of a facultative anaerobe
Escherichia coli (E. coli)
375
why are facultative anaerobes so successful
They can survive and grow with or without oxygen
376
Can aerotolerant anaerobes tolerate oxygen?
Yes
377
Do aerotolerant anaerobes use oxygen for energy?
No, they choose not to use oxygen
378
What type of metabolism do aerotolerant anaerobes use?
Fermentation
379
What are aerotolerant anaerobes also called?
Obligate fermenters
380
What metabolic pathway do aerotolerant anaerobes use?
Glycolysis only
381
How much ATP do aerotolerant anaerobes produce?
2 ATP
382
Give an example of an aerotolerant anaerobe.
Lactobacillus species
383
What product is produced by Lactobacillus species?
Lactic acid
384
What is the key feature that defines aerotolerant anaerobes?
They tolerate oxygen but do not use it
385
Do microaerophiles use oxygen?
Yes
386
How much oxygen do microaerophiles require?
Only small amounts
387
What is the key feature that distinguishes microaerophiles?
They need low oxygen levels
388
What metabolic pathways do microaerophiles use?
Glycolysis and Krebs cycle
389
How does their energy yield compare to aerobic organisms?
Similar to 38 ATP
390
How do microaerophiles grow under appropriate conditions?
They grow very well but require low oxygen levels
391
Where do microaerophiles grow in a tube?
In the middle
392
Do microaerophiles grow at the top or bottom of the tube?
No — not high, not low
393
Are microaerophiles aerobic?
Yes, but they require small amounts of oxygen
394
Name a microaerophile that causes ulcers.
Helicobacter pylori
395
Name a microaerophile that causes gastroenteritis.
Campylobacter jejuni
396
Where is Campylobacter jejuni commonly found?
Undercooked chicken
397
What are bacteria called that cannot grow in the presence of oxygen?
Anaerobes
398
What are bacteria that grow only in the absence of oxygen sometimes called?
Anaerobes or fermenters
399
How do microaerophiles differ from obligate aerobes?
They require oxygen, but only at low concentrations
400
Why can oxygen be dangerous to cells?
Oxygen produces toxic forms
401
What are toxic oxygen species?
Reactive forms of oxygen that can damage cells
402
Name toxic oxygen species listed in the notes.
Singlet oxygen and superoxide free radicals
403
What are superoxide free radicals?
Highly reactive oxygen
404
Why are superoxide free radicals dangerous?
They steal electrons from other molecules
405
What happens to oxygen when it becomes a superoxide free radical?
Oxygen is raised to a higher energy state
406
What must happen to toxic oxygen species?
They must be completely neutralized
407
How does the cell begin neutralizing toxic oxygen species?
Combine oxygen with hydrogen ions
408
What molecule is formed during this process?
Hydrogen peroxide
409
What happens to hydrogen peroxide after catalase or peroxide acts on it?
It is neutralized further to lower energy states
410
Why do some bacteria struggle to survive in oxygen?
They cannot neutralize toxic oxygen species
411
Why is molecular oxygen (O₂) considered toxic despite being essential for life?
It is a poisonous gas that can form highly reactive toxic oxygen derivatives.
412
Why might life not have arisen if oxygen had been present early in Earth’s history?
Because molecular oxygen is toxic to early life forms.
413
Why does aerobic respiration yield a lot of energy?
Hydrogen atoms stripped from organic compounds combine with oxygen to form water, releasing large amounts of energy.
414
Which microbes extract more energy from nutrients: aerobes or anaerobes?
Aerobes.
415
What are organisms that require oxygen to live called?
Obligate aerobes.
416
Why are obligate aerobes at a disadvantage in aquatic environments?
Oxygen is poorly soluble in water.
417
What are facultative anaerobes?
Organisms that can use oxygen when present but can grow without it using fermentation or anaerobic respiration.
418
What happens to energy production in facultative anaerobes when oxygen is absent?
Energy production efficiency decreases.
419
Give an example of a facultative anaerobe found in humans.
Escherichia coli in the intestinal tract.
420
How do yeasts typically produce energy when growing anaerobically?
Fermentation.
421
What defines anaerobes?
They cannot use molecular oxygen for energy-yielding reactions.
422
How does oxygen affect most obligate anaerobes?
It harms or kills them.
423
Which genus includes bacteria that cause tetanus and botulism?
Clostridium.
424
How does Clostridium obtain energy?
Anaerobic respiration.
425
What enzyme helps detoxify hydrogen peroxide?
Catalase
426
What does catalase act on?
Hydrogen peroxide (H₂O₂)
427
What does catalase convert hydrogen peroxide into?
Water and oxygen
428
What are superoxide radicals (superoxide anions)?
Toxic free radicals formed during normal oxygen respiration.
429
Why are superoxide radicals dangerous?
They are highly unstable and steal electrons from nearby molecules.
430
What enzyme neutralizes superoxide radicals?
Superoxide dismutase (SOD).
431
Why is hydrogen peroxide toxic?
It contains the peroxide anion (O₂²⁻).
432
What enzyme converts hydrogen peroxide into water and oxygen?
Catalase.
433
What is the catalase reaction?
2 H₂O₂ → 2 H₂O + O₂
434
How can catalase be detected in bacteria?
Oxygen bubbles form when hydrogen peroxide is added.
435
How does peroxidase differ from catalase?
It breaks down hydrogen peroxide without producing oxygen.
436
How are toxic oxygen forms used by the immune system?
They help kill pathogens during phagocytosis.
437
Where are pathogens exposed to toxic oxygen compounds during phagocytosis?
Inside the phagolysosome.
438
Why are obligate anaerobes extremely oxygen-sensitive?
They produce neither SOD nor catalase, allowing toxic radicals to accumulate.
439
What enzyme also neutralizes hydrogen peroxide?
Peroxidase
440
What is the function of peroxidase?
Neutralizes hydrogen peroxide
441
Why is oxygen such an important determinant of microbial growth?
Growth depends on whether the organism has enzymes to handle toxic oxygen byproducts
442
What determines whether an organism can survive in oxygen?
The presence of detoxification enzymes (e.g., catalase, peroxidase)
443
Why can obligate anaerobes not survive in oxygen?
They lack enzymes to detoxify toxic oxygen byproducts
444
What are aerotolerant anaerobes?
Fermentative bacteria that cannot use oxygen but tolerate it.
445
Why can aerotolerant anaerobes survive in oxygen?
They possess SOD or equivalent systems to neutralize toxic oxygen forms.
446
Give a common example of aerotolerant anaerobes.
Lactobacilli used in fermented foods.
447
What is the goal of pure culture techniques?
To obtain pure (individual) colonies
448
Why are organisms replated?
To separate and isolate individual organisms
449
What culture method is used to obtain pure colonies?
Streak plate method
450
What does the streak plate method produce?
Clear, isolated colonies
451
Why do you never want a mixed colony?
Mixed colonies contain more than one organism
452
What type of colonies are desired for identification?
Clear, isolated colonies
453
How is a streak plate performed?
By streaking the plate
454
Why is the streak plate method important in microbiology?
It allows isolation of individual organisms to create a pure culture
455
What are microaerophiles?
Aerobic bacteria that require oxygen at concentrations lower than atmospheric levels.
456
Where do microaerophiles grow in a test tube?
At a depth where small amounts of oxygen have diffused.
457
Why can’t microaerophiles grow in oxygen-rich environments?
They produce lethal levels of superoxide radicals and peroxides.
458
What is a biofilm?
A thin, slimy layer of bacteria encased in extracellular material and attached to a surface.
459
Why are biofilms medically significant?
They are up to 1000× more resistant to microbicides.
460
What percentage of human bacterial infections involve biofilms?
~70%.
461
Which medical devices commonly develop biofilms?
Catheters and other indwelling devices.
462
What is the purpose of selective media?
Selects for desired organisms
463
What else does selective media do?
Inhibits unwanted organisms
464
Give an example of a selective medium.
Bismuth sulfide
465
What organism is bismuth sulfide used to grow?
Salmonella typhi
466
What disease is caused by Salmonella typhi?
Typhoid fever
467
How serious is typhoid fever?
Deadly infection
468
In which populations is typhoid fever most commonly seen (as written)?
Immigrants / new populations
469
How is Salmonella typhi spread?
Food, water, feces, and urine
470
If nothing grows on selective media, what does this indicate?
The patient is not sick with what you suspected
471
What does selective media leave behind?
It shows the organism you’re testing for, if nothing grows - your pt is not sick with what you thought
It selects who can grow, and inhibits or kills the growth of others
It leaves behind the desired organisms, and inhibits the growth of others
472
Why is selective media useful in diagnosis?
It suppresses unwanted organisms so target organisms can grow
473
What is the purpose of differential media?
To distinguish organisms based on biochemical reactions
474
What is an example of differential media?
Blood agar
475
What organism is commonly grown on blood agar in this context?
Streptococcus pyogenes
476
How many possible zones can be seen on blood agar?
Three
477
What does a clear zone around colonies indicate?
Hemolysis
478
What happens to the blood in a clear zone?
Blood is completely destroyed in that region
479
What does a clear zone on blood agar indicate for strep?
Strep positive
480
What type of hemolysis does Streptococcus pyogenes show?
Complete hemolysis (clear zones)
481
What is combined selective and differential media?
Media that both inhibits some organisms and differentiates others
482
What is an example of combined selective and differential media?
Mannitol salt agar
483
What makes mannitol salt agar selective?
Salt
484
What makes mannitol salt agar differential?
Mannitol
485
What organism is mannitol salt agar used to grow?
Staphylococcus aureus
486
What types of infections does Staphylococcus aureus cause?
Skin infections (TSF as written)
487
What does a yellow zone on mannitol salt agar indicate?
Mannitol fermentation
488
What causes the color change to yellow on MSA?
Acid production from mannitol fermentation
489
What is the streak plate method?
A fundamental microbiology laboratory technique.
490
What is the main purpose of the streak plate method?
To isolate and cultivate pure bacterial colonies from a mixed sample.
491
Why is the streak plate method essential?
It is essential for accurate identification, diagnosis, and re-isolation of bacteria.
492
What is the goal of separating individual bacterial cells in the streak plate method?
So they grow into discrete (isolated) colonies.
493
Why must mixed growth be prevented on a streak plate?
To allow identification of a single bacterial species.
494
When must the inoculating loop be sterilized?
Before the initial streak and between each streaked region.
495
Why is the inoculating loop sterilized between streaked regions?
To prevent cross-contamination between regions.
496
How is the streak plate applied to the agar plate?
The plate is streaked in sequential regions.
497
How many streaking motions should typically be used per region?
Only twice per region.
498
Why should streaking motions be limited in each region?
To prevent excessive overlap and overcrowding.
499
What happens if over-streaking occurs?
Colonies merge, making isolation impossible.
500
What type of bacterial growth is seen in the first streaked region?
Dense bacterial growth.
501
What happens to bacterial growth in subsequent streaked regions?
There are progressively fewer bacteria and more isolated colonies.
502
Where are individual, isolated colonies most likely to appear?
In the later streaked regions.
503
How should the agar surface be handled during streaking?
Avoid breaking or damaging the agar surface.
504
Why must the agar surface remain intact?
Intact agar supports optimal colony formation.
505
What is the effect of gouging the agar?
It interferes with bacterial growth and interpretation.
506
Why are isolated (discrete) colonies important?
They are essential for diagnostic accuracy.
507
Why are discrete colonies required when identifying bacteria?
They allow identification of different bacterial species.
508
Why are isolated colonies necessary in mixed infections?
They are required for re-isolating organisms from mixed infections.
509
Can mixed colonies be used for bacterial identification?
No. Mixed colonies must never be used for identification.
510
colony morphology
The visible growth patterns produced by bacteria.
511
Why is colony morphology important in diagnostics?
It can provide visual clues to bacterial identity.
512
Do different bacteria produce the same colony morphology?
No. Different bacteria produce different visible growth patterns.
513
What are examples of colony morphology patterns?
Grape-like clusters and fan-shaped growth.
514
What type of colonies are required for accurate bacterial identification?
Isolated, pure colonies.
515
Why are pure cultures required for diagnosis?
They allow accurate identification of the causative pathogen and ensure proper treatment.
516
What does mixed colony morphology indicate?
The presence of multiple bacterial types.
517
What must be done if multiple colony types are present on a plate?
Each unique colony type must be separately processed.
518
Why must different colony types be re-plated?
To obtain pure isolates for further analysis.
519
What is selective media designed to do?
Inhibit unwanted bacteria and promote growth of specific organisms.
520
What is an example of selective media?
Bismuth sulfite agar.
521
What organism is bismuth sulfite agar selective for?
Salmonella typhi.
522
How does bismuth sulfite agar function?
It inhibits competing bacteria.
523
What disease is diagnosed using bismuth sulfite agar?
Typhoid fever.
524
How is Salmonella typhi transmitted?
Through food, water, feces, and urine.
525
Which populations have a higher prevalence of typhoid fever?
Immigrants or newcomers from endemic areas.
526
What does no growth on selective media indicate?
The suspected pathogen is not present.
527
When is differential media used?
When selective isolation is not possible.
528
What is the purpose of differential media?
To differentiate organisms based on biochemical reactions.
529
What is an example of differential media?
Blood agar.
530
How does blood agar differentiate bacteria?
Based on hemolysis.
531
What organism produces clear hemolytic zones on blood agar?
Streptococcus pyogenes.
532
What does a clear hemolytic zone indicate?
A positive strep result.
533
How is strep throat diagnosed using culture media?
A throat swab is plated on blood agar.
534
What confirms Streptococcus pyogenes infection?
Clear hemolytic zones on blood agar.
535
Why is diagnosis delayed when using culture methods?
Due to culture growth time and verification requirements.
536
What media is both selective and differential?
Mannitol salt agar.
537
Why is mannitol salt agar selective?
High salt concentration inhibits most bacteria.
538
Which bacteria can grow on mannitol salt agar?
Staphylococcus species.
539
How does mannitol salt agar differentiate bacteria?
Based on mannitol fermentation.
540
What organism ferments mannitol on mannitol salt agar?
Staphylococcus aureus.
541
What indicates mannitol fermentation on the agar?
A yellow zone.
542
What is mannitol salt agar used for clinically?
Rapid diagnosis, MRSA identification, and food poisoning investigations.
543
What culture media is used when typhoid is suspected?
Bismuth sulfite agar.
544
What condition is blood agar primarily used to diagnose?
Strep throat.
545
What culture media is used for skin and soft tissue infections?
Mannitol salt agar.
546
What culture media is used for food safety concerns?
Mannitol salt agar.
547
What is binary fission?
Method of bacterial cell division
548
What happens to the bacterial cell during binary fission?
The cell multiplies, then breaks apart
549
What is the “two whiteboard markers” example meant to show?
One cell splitting into two identical cells
550
How fast does binary fission occur?
Very quickly
551
Where does binary fission commonly occur?
In the lab
552
Why can patients get sick very quickly from bacterial infections?
Because bacteria divide rapidly by binary fission
553
What is the growth pattern of bacteria during binary fission?
Doubling pattern
554
What happens after one round of binary fission?
1 → 2 cells
555
What happens after two rounds of binary fission?
2 → 4 cells
556
What happens after three rounds of binary fission?
4 → 8 cells
557
What mathematical pattern describes bacterial growth?
Powers of 2
558
What does 2⁰ equal?
1
559
What does 2¹ equal?
2
560
What does 2² equal?
4
561
Does the pattern continue?
Yes
562
Why does bacterial population size increase so rapidly?
Because binary fission follows a doubling (power of 2) pattern
563
What is generation time?
The time it takes for one cell to divide.
564
What does one generation represent?
One doubling.
565
How is generation time described numerically (as written)?
Time from 0 → 1.
566
Is generation time variable or constant?
Constant.
567
Is the time the same for each cell division?
Yes.
568
Are calculation questions required for generation time?
No.
569
Do you need to know or use an equation for generation time?
No.
570
What is the key idea to remember about generation time?
Bacteria divide at a constant rate, doubling each generation.
571
What happens to cell number during the lag phase?
No increase in cell number
572
Are colonies visible during the lag phase?
No colonies
573
What does the log phase look like on a growth graph?
Straight line
574
What pattern do cell numbers follow in log phase?
Multiples of 2
575
Give an example of cell doubling in log phase.
1 → 2 → 4 → 8
576
What does the log phase demonstrate?
Generation time
577
How are cells during the log phase in terms of vulnerability?
Cells are most vulnerable
578
When is the best time to apply antibiotics?
Log phase
579
When is the best time to apply chemicals?
Log Phase
580
Do new cells still form during the stationary phase?
Yes
581
What is happening to nutrients during the stationary phase?
Nutrients are in short supply
582
Why can cells not grow further in stationary phase?
Limited nutrients
583
Is there a visible change in total cell number during stationary phase?
No
584
What happens to cells during the death phase?
Cells begin to die off
585
Why is the death phase desirable in a patient?
It indicates the infection is being eliminated
586
Each cell death ___
___
587
Why do we move from broth to Petri dishes?
To see colonies
588
How do organisms get onto a Petri dish?
Transfer from broth → Petri dish
589
What is added to liquid broth to make a solid medium?
Agar
590
What is agar?
A complex polysaccharide
591
What analogy is used to describe agar?
Like gelatin used in painting, but much more powerful
592
What is the main purpose of agar?
Solidifying agent
593
What does agar do to liquid broth?
Makes it solid
594
What does agar provide for microbial growth?
A solid background
595
What does a solid background allow you to do?
See colonies and obtain pure cultures
596
Can organisms use agar as food?
No
597
Can organisms dissolve agar?
No
598
Why is it good that bacteria cannot break down agar?
The solid medium remains intact
599
At what temperature does agar melt?
~100°C
600
Why is agar’s melting temperature useful?
It is near sterilization temperature
601
What must be done after agar melts?
It must be cooled before pouring
602
How is molten agar cooled before pouring?
In a water bath
603
To what temperature should agar be cooled before pouring?
~45°C
604
Why is 45°C ideal for pouring agar?
Cool enough to pour but still liquid
605
Where is molten agar poured?
Plates / Petri dishes
606
What happens to gelatin at room temperature?
It melts
607
What happens to agar at room temperature and 37°C?
Becomes solid and remains solid
608
Why is 37°C important in microbiology?
Perfect temperature for bacterial growth
609
What do agar plates allow you to visualize?
Colonies
610
What do agar plates allow you to isolate?
Individual organisms
611
Why are agar plates best for pure cultures?
They allow isolation and clear colony growth
612
Are nutrient broth cultures good for diagnosis?
No
613
Why are agar plates better for diagnosis?
They show colonies clearly
614
How are agar plates used clinically?
To identify organisms and infections
615
How is diagnosis done in the lab?
By identifying colonies on agar plates
616
What is the best way to grow organisms for identification?
Agar plates
617
What are broth cultures mainly used for?
Growth only, not diagnostic
618
What is binary fission?
The primary method of bacterial cell division.
619
What happens during binary fission?
One bacterial cell divides into two identical cells.
620
What type of growth results from binary fission?
Exponential (logarithmic) growth.
621
How does the bacterial population change with each division?
The population doubles.
622
What is the doubling pattern seen in exponential growth?
1 → 2 → 4 → 8 → 16 → etc.
623
How does bacterial growth change over time?
Growth accelerates rapidly.
624
Starting from one bacterial cell, what can the population reach after 20 divisions?
Approximately 1.048 million cells.
625
What does this example demonstrate clinically?
How quickly bacterial infections can escalate in the body.
626
What is generation time?
The time required for one cell to complete binary fission.
627
What else does generation time represent?
The time required for a population to double.
628
Is generation time the same for all organisms?
No. It is typically constant for a given organism.
629
What factors affect generation time?
Environmental conditions.
630
How long can generation time be?
It can range from seconds upward depending on the organism.
631
Why are rapid generation times clinically important?
They explain why infectious diseases progress quickly in patients.
632
Why is bacterial growth best visualized using a logarithmic scale?
Because bacterial growth is exponential in nature.
633
How does the exponential phase appear on a logarithmic scale?
As a straight line.
634
Why is a logarithmic scale useful for analyzing bacterial growth?
It makes analysis easier and more informative.
635
When does the lag phase occur?
Immediately after inoculation (right after bacteria is placed into a new environment)
636
Is there an increase in cell number during the lag phase?
No visible increase in cell number occurs.
637
Are cells metabolically active during the lag phase?
Yes.
638
What metabolic activities occur during the lag phase?
Synthesizing ATP, producing enzymes, and adapting to the environment.
639
Is the lag phase a dormant phase?
No.
640
What are cells preparing for during the lag phase?
Cell division.
641
What characterizes the log phase?
Rapid cell division.
642
How does the population change during the log phase?
It increases exponentially.
643
What happens to each cell during the log phase?
Each cell divides into two, creating a consistent doubling pattern.
644
Why is the log phase critical in medicine?
Cells are most vulnerable during this phase.
645
What are bacterial cells most vulnerable to in the log phase?
Antibiotics and sterilization techniques.
646
What practical interventions are most effective during the log phase?
Hand sanitizers and irradiation.
647
When does the stationary phase occur?
When nutrients become limited and waste products accumulate.
648
What happens to cell division and cell death during the stationary phase?
The rate of cell division equals the rate of cell death.
649
How does the population size change in the stationary phase?
It remains stable.
650
In laboratory settings, what growth phase are plate cultures often assumed to be in?
The stationary phase.
651
What does the stationary phase reflect on solid media?
Nutrient limitations.
652
What defines the death (logarithmic decline) phase?
The cell death rate exceeds new cell formation.
653
What happens to the bacterial population during the death phase?
The overall population decreases.
654
How does cell death occur in this phase?
Logarithmically.
655
What is the goal of antibiotic treatment in relation to the growth curve?
To push bacteria into the death phase.
656
How do antibiotics reduce bacterial populations?
By causing ineffective reproduction, leading to population decline.
657
Why is understanding bacterial growth phases important?
For infection control, food spoilage prevention, food preservation, and industrial microbiology.
658
How are growth phases used in the food industry and fermentation?
The log phase is used as a reference for process optimization.
659
During which growth phase are bacteria most vulnerable?
The log (exponential) phase.
660
What are cells in the log phase most susceptible to?
Antibiotics, chemical controls, and alcohol-based hand rubs.
661
Why are hygiene practices most effective during the log phase?
Because bacteria are actively dividing.
662
What sterilization method was linked to real-world applications?
Irradiation.
663
What are examples of items sterilized by irradiation?
Gloves and catheter kits.
664
Why are gloves and catheter kits considered sterile?
They are irradiated to achieve microbial control.
665
Why is understanding bacterial growth critical in medical and health professions?
It informs timely antibiotic use, proper sterilization practices, and infection control strategies.
666
Which growth phase was repeatedly emphasized as the best target for interventions?
The log phase.
667
What interventions are most effective during the log phase?
Personal hygiene (handwashing, hand sanitizer), medical device sterilization, and antibiotic treatment.
668
What additional areas apply knowledge of bacterial growth phases?
Food safety, fermentation technologies, preventing spoilage, and optimizing beneficial microbial processes.
669
What are selective media used for?
To suppress unwanted bacteria and encourage growth of desired microbes.
670
How do selective media work?
They contain agents that inhibit certain organisms while allowing others to grow.
671
What is bismuth sulfite agar selective for?
Salmonella Typhi.
672
What does bismuth sulfite inhibit?
Gram-positive bacteria and most gram-negative intestinal bacteria.
673
What is Sabouraud’s dextrose agar selective for?
Fungi.
674
Why does Sabouraud’s agar favor fungi?
Its low pH (≈5.6) inhibits most bacteria.
675
What are differential media used for?
To distinguish colonies of different organisms on the same plate.
676
How do differential media distinguish bacteria?
By visible reactions (e.g., color change, hemolysis).
677
What makes blood agar a differential medium?
It shows hemolysis of red blood cells.
678
What does a clear zone around colonies on blood agar indicate?
Beta-hemolysis (lysis of red blood cells).
679
Which bacterium commonly shows beta-hemolysis on blood agar?
Streptococcus pyogenes.
680
Can selective and differential characteristics be combined in one medium?
Yes.
681
What medium is used to isolate Staphylococcus aureus?
Mannitol salt agar (MSA).
682
Why can Staphylococcus aureus grow on mannitol salt agar?
It tolerates high sodium chloride.
683
What concentration of NaCl is in mannitol salt agar?
7.5% sodium chloride.
684
What makes mannitol salt agar selective?
High salt inhibits most bacteria but not Staphylococcus spp.
685
What makes mannitol salt agar differential?
It contains mannitol and a pH indicator.
686
What metabolic ability differentiates S. aureus on MSA?
Fermentation of mannitol to acid.
687
What happens to the medium when mannitol is fermented?
The color changes (to yellow).
688
What does growth plus color change on MSA indicate?
Likely Staphylococcus aureus.
689
What happens when mixed samples are plated on solid medium?
Colonies form.
690
What is a bacterial colony?
A visible population of cells identical to the original organism.
691
A colony theoretically arises from what?
A single spore, vegetative cell, or a clump of identical cells.
692
Why do colonies need to be well separated on a plate?
To distinguish individual colonies.
693
What is required for most bacteriological work?
Pure cultures (clones).
694
What is a pure culture?
A culture containing only one type of bacterium.
695
What is the most common method used to obtain pure cultures?
The streak plate method.
696
What is the purpose of streaking bacteria across the agar surface?
To dilute cells so isolated colonies can form.
697
Why do colonies form only in later streaks?
Cells are spread far enough apart.
698
What is done with isolated colonies?
Picked up and transferred to fresh medium to form a pure culture.
699
What happens to cell number during the lag phase?
Changes very little or not at all.
700
Why don’t cells divide immediately in a new medium?
They are adjusting to the new environment.
701
Are cells dormant during the lag phase?
No.
702
What are cells doing metabolically during the lag phase?
Intense metabolic activity, including enzyme synthesis.
703
How long can the lag phase last?
From about 1 hour to several days.
704
What defines the log phase?
Rapid cell division with exponential growth.
705
What happens to generation time during the log phase?
It reaches a constant minimum.
706
Why is a logarithmic growth curve a straight line during the log phase?
Because generation time is constant.
707
When are cells most metabolically active?
During the log phase.
708
Why is the log phase important industrially?
It is when cells or their products are produced most efficiently.
709
What happens during the death phase?
Cell deaths exceed the formation of new cells.
710
What is another name for the death phase?
Logarithmic decline phase.
711
What happens to the population during the death phase?
It decreases to a tiny fraction of the previous population or dies out entirely.
712
Do all species die out completely in the death phase?
No, some retain surviving cells almost indefinitely.
713
What factor differentiates microbes into five groups based on preferred range?
Temperature.
714
How are microbes classified by temperature?
Into five groups based on preferred temperature range.
715
What temperature limits do microbes exhibit?
Minimum growth temperature, optimum growth temperature, and maximum growth temperature.
716
What is the minimum growth temperature?
The lowest temperature at which a microbe can grow.
717
What is the optimum growth temperature?
The temperature at which growth rate is highest.
718
What is the maximum growth temperature?
The highest temperature at which a microbe can grow.
719
How does growth rate change with temperature (based on the graph)?
Growth increases to an optimum, then drops sharply past the maximum temperature.
720
What pH range do most bacteria grow best in?
pH 6.5–7.5
721
What pH range do molds and yeasts grow best in?
pH 5–6
722
Compared to bacteria, do molds and yeasts prefer more acidic or neutral conditions?
More acidic
723
What is osmotic pressure based on?
The solute concentration of the environment
724
What are the three osmotic conditions microbes experience?
Isotonic, hypertonic, hypotonic
725
What does isotonic mean?
Equal solute concentration inside and outside the cell
726
What does hypertonic mean?
Higher solute concentration outside the cell
727
What does hypotonic mean?
Lower solute concentration outside the cell
728
What is plasmolysis?
Shrinkage of the cytoplasm due to water leaving the cell
729
In what type of solution does plasmolysis occur?
Hypertonic solution
730
What happens to water during plasmolysis?
Water moves out of the cell
731
What happens to the plasma membrane during plasmolysis?
It pulls away from the cell wall
732
Does plasmolysis inhibit cell growth?
Yes
733
What is happening in an isotonic solution (≈0.85% NaCl)?
No net water movement; cell remains normal
734
What is happening in a hypertonic solution (e.g., 10% NaCl)?
Water leaves the cell → plasmolysis
735
What is the ONE thing to remember about plasmolysis?
High solute outside the cell causes water loss and inhibits growth
736
What chemical factor is being introduced here?
Oxygen availability
737
Is oxygen essential for all life forms?
No — only for humans and some bacteria
738
Can some bacteria grow without oxygen?
Yes
739
What does oxygen availability determine in bacteria?
Their growth capability and metabolic type
740
What is the key idea of this slide?
Not all bacteria require oxygen to grow
741
What type of growth do obligate aerobes have?
Only aerobic growth; oxygen required
742
Where do obligate aerobes grow in a tube?
At the top (high oxygen area)
743
Why do obligate aerobes grow only at the top?
Oxygen diffuses from the surface
744
What enzymes do obligate aerobes have?
Catalase and superoxide dismutase (SOD)
745
What do these enzymes do?
Neutralize toxic forms of oxygen
746
What type of growth do facultative anaerobes have?
Both aerobic and anaerobic growth
747
Where is growth greatest for facultative anaerobes?
Where oxygen is present
748
Where do facultative anaerobes grow in a tube?
Throughout the tube, but most at the top
749
What enzymes do facultative anaerobes have?
Catalase and superoxide dismutase (SOD)
750
Why can they grow with or without oxygen?
They can neutralize toxic oxygen and use oxygen when available
751
What type of growth do obligate anaerobes have?
Only anaerobic growth
752
What happens to obligate anaerobes in the presence of oxygen?
Growth ceases
753
Where do obligate anaerobes grow in a tube?
At the bottom (no oxygen)
754
Why do obligate anaerobes avoid oxygen?
They lack enzymes to neutralize toxic oxygen
755
Do obligate anaerobes tolerate oxygen?
No
756
What type of growth do aerotolerant anaerobes have?
Only anaerobic growth
757
Can aerotolerant anaerobes survive in oxygen?
Yes, but they do not use it
758
Where do aerotolerant anaerobes grow in a tube?
Evenly throughout the tube
759
Why does oxygen not affect aerotolerant anaerobes?
They can partially neutralize toxic oxygen
760
What enzyme do aerotolerant anaerobes have?
Superoxide dismutase (SOD) only
761
What type of growth do microaerophiles have?
Aerobic growth at low oxygen levels
762
Do microaerophiles require oxygen?
Yes, but only in low concentration
763
Where do microaerophiles grow in a tube?
Just below the surface
764
What happens if microaerophiles are exposed to normal oxygen levels?
They produce lethal amounts of toxic oxygen
765
Which bacteria grow only at the top of a tube?
Obligate aerobes
766
Which bacteria grow everywhere but most at the top?
Facultative anaerobes
767
Which bacteria grow only at the bottom?
Obligate anaerobes
768
Which bacteria grow evenly throughout the tube?
Aerotolerant anaerobes
769
Which bacteria grow just below the surface?
Microaerophiles
770
What is singlet oxygen?
O₂ boosted to a higher-energy state
771
Name one type of toxic oxygen molecule.
Superoxide free radical
772
Name another toxic oxygen molecule.
Peroxide anion
773
What is the hydroxyl radical?
OH•
774
List the four toxic forms of oxygen.
Singlet oxygen
Superoxide free radical
Peroxide anion
Hydroxyl radical (OH•)
775
What is a culture medium?
Nutrients prepared for microbial growth
776
What does sterile mean?
No living microbes
777
What is an inoculum?
Introduction of microbes into a medium
778
What is a culture?
Microbes growing in nutrient broth or on an agar plate
779
What is agar?
A complex polysaccharide
780
What is agar used for in microbiology?
Solidifying agent for culture media in Petri plates
781
Is agar metabolized by microbes?
No
782
At what temperature does agar liquefy?
100 °C
783
At what temperature does agar remain solid?
~37 °C
784
Why is agar ideal for culturing microbes?
It solidifies media, is not metabolized by microbes, and stays solid at body temperature (~37 °C)
785
What does a pure culture contain?
Only one species or strain
786
What is a colony?
A population of cells arising from a single cell or spore, or from a group of attached cells
787
What method is used to isolate pure cultures?
The streak plate method
788
Why is the streak plate method used?
To isolate pure cultures
789
What is the purpose of selective media?
Suppress unwanted microbes and encourage desired microbes
790
What do selective media do to unwanted microbes?
Inhibit their growth
791
What do selective media do to desired microbes?
Encourage their growth
792
What is the key idea behind selective media?
They inhibit some microbes while allowing others to grow
793
What is the purpose of differential media?
To make it easy to distinguish colonies of different microbes
794
What does differential media allow you to see?
Visible differences between colonies growing on the same plate
795
Key difference between selective vs differential media?
Selective: inhibits some microbes
Differential: distinguishes between microbes that grow
796
What do selective and differential media do?
Suppress unwanted microbes and make it easy to distinguish colonies
797
What is the selective role of selective & differential media?
Suppress unwanted microbes
798
What is the differential role of selective & differential media?
Make it easy to distinguish colonies
799
What is an example of selective and differential media?
Mannitol Salt Agar
800
What is binary fission?
Asexual cell division in bacteria
801
Step 1 of binary fission?
Cell elongates and DNA is replicated
802
Step 2 of binary fission?
Cell wall and plasma membrane begin to constrict
803
Step 3 of binary fission?
Cross-wall forms, completely separating the two DNA copies
804
Step 4 of binary fission?
Cells separate
805
Where is bacterial DNA located during binary fission?
Nucleoid
806
What structures constrict during binary fission?
Cell wall and plasma membrane
807
What is the end result of binary fission?
Two genetically identical cells
808
What are the four phases of the bacterial growth curve (in order)?
Lag → Log (exponential) → Stationary → Death
809
What happens during the lag phase?
Cells are metabolically active but not increasing in number
810
What are bacteria doing in the lag phase?
Adapting to environment; synthesizing enzymes and cell components
811
What defines the log phase?
Rapid, exponential increase in population
812
How do bacteria reproduce in the log phase?
Binary fission
813
Why is log phase important clinically?
Cells are most metabolically active and most susceptible to antibiotics
814
What happens during the stationary phase?
Rate of cell division = rate of cell death
815
Why does growth stop increasing in stationary phase?
Nutrients depleted + waste products accumulate
816
What happens during the death phase?
Population decreases at a logarithmic rate
817
Why do cells die in this phase?
Lack of nutrients and toxic waste buildup
818
What is on the x-axis of the bacterial growth curve?
Time
819
What is on the y-axis of the bacterial growth curve?
Log of number of bacteria
820
Which phase shows the fastest growth?
Log phase
821
Which phase is best for studying metabolism and antibiotic effects?
Log phase
822
Which phase shows equilibrium?
Stationary phase
Microbiology
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