Flashcards in Bacterial Disease Testing Deck (73):
Cultures are performed for a variety of reasons.
1. Confirm a diagnosis
2. Exclude a diagnosis
4. Monitor the course of a disease
5. Monitor response to therapy
6. Stage the severity of the disease
7. Provide a prognosis
As a general rule infection considered if how many organisms are found?
Anything less than what is contaminated?
What are you counting?
>10^5 Organisms found
Whats a more common causitive agent, pure isolate or mixed flora?
What question do we want to ask when we treat?
1. Is the organism isolated known to cause disease at this site?
2. Special considerations for immunocompromised
How long does it take to gro the organism and identify it?
A preliminary report for most cultures is usually issued when?
1. 1 full day to grow the organism and then
2. part or all of 1 day to identify it.
It may take an additional day to isolate it before identification if there is a mixture of organisms.
A preliminary report for most cultures may be issued in 24 hours
Normal flora of the skin?
1. Staph epidermidis,
2. S. aureus,
4. few gram neg bacilli moist skin, 5. Corynebacterium,
6. Propionibacterium acnes
Pathogenic bacteria of the skin?
Pathogenic bacteria of the mouth?
1. Strep pneumoniae,
2. Strep pyogenes,
3. Neisseria meningitidis,
4. Haemophilus influenza,
5. Neisseria gonorrheae
Potential pathogens of the oropharynx?
Definite pathogens of the oropharynx?
2. Bordatella pertussis,
1. Staph aureus
NOrmal flora of the conjunctiva? 4
Pathogenic bacteria of the conjunctiva?3
4. Staph and Strep,
occasional Haemophilus and Parainfluenza
Pathogenic bacteria of the GI tract?
1. Clostridium difficile,
3. toxic strains E. coli,
4. Helicobacter pylori (in duodenum)
Pathogenic bacteria of the Anterior Urethra
Chlamydia, Gonorrhea, Syphilis
Pathogenic bacteria of the Vagina?
Losing normal flora and allowing these to grow
Should we obtain a specimen/culture before or after antibiotics are administered?
When should pathogens arrive at the lab after collection?
1-2 hours after collection
What lab samples should not be refrigerated?
3. joint fluid and
4. cervical secretions for gonorrhea
Culture Turnaround Times:
Most routine cultures (urine, throat, sputum)?
1. Blood cultures: 48-96 hours
2. Most routine cultures (urine, throat, sputum) 24-48 hrs; unless looking for unusual bacteria
3. Anaerobes: can take 48-72 hours
What test are we getting almost everytime we are culturing a bacteria?
What is our routine culture media?
What kind of culture medium do gram negatives like GC and Haemophilus sp. grow on?
What should we remember about anaerobic blood agar?
What does fungi grow on?
Needs to be fresh
What is a gram positive selective media - allows isolation of strep ; staph ; inhibits most gram neg. rods?
Anaerobic gram negative rods grow on what kind of agar? 2
What is a liquid media, enrichment broth used as a supplement to plated media?
MacConkey or eosin methylene blue agars
What is usually present in a Wound Culture?
What area should we culture for a wound? (whats most accurate?)
Culture of specimens from the skin edge is less accurate than culturing the suppurative material
When we are culturing an Abscess/boil/furuncle what is the process and where do we need to culture it?
1. Incised and any fluid or material swabbed with culture swab and sent to lab
2. Important to get pus/exudate from deep in the wound to avoid surface contamination
Must incise and get deep into the wound
Describe the process of collecting a culture from the eye-conjuctiva?
(at what temperature should we send the eye culture to the lab?)
Gently swab to collect drainage
Place in appropriate container and send to lab at 25 degrees C
Throat cultures are generally obtained to rule out what?
strep pharyngitis (GABS).
For throat cultures you need to tell the lab if you are look for a different kind of bacteria like N. Gonnorhea. What does that need to grow on?
What area of the throat do we swab?
What temp do we send it to the lab at?
Swab posterior pharynx and tonsils (if present)
Avoid touching any other part of the mouth
25 degree C
Sputum culture indications
1. Hospital-acquired pneumonia (HAP)
2. Hospitalized patients with pneumonia (CAP) and any of the following criteria:
-Failure of outpatient antibiotic therapy
-Active alcohol use
-Severe obstructive of structural lung disease
-Positive urine antigen test for Pneumococcus
-Positive urine antigen test for Legionella
Sputum cultures are NOT indicated in the following?
1. For most outpatient community acquired pneumonias
2. Management of bronchitis
3. Initial management of acute exacerbations of COPD
Describe the process for sputum collection for optimal yield?
1. Obtain prior to antibiotic treatment
2. Have the patient rinse their mouth prior to expectoration
3. No food 1-2 hours prior to expectoration
4. Inoculation of the culture media immediately after the specimen if obtained or immediately after prompt transport to the microbiology lab
What is a sampling of the lower airway is another potential diagnostic method in patients w/ suspected pneumonia?
What would make a sputum culture inaccurate?
What would make us suspect a pathogen in a sputum culture?
Suspect a pathogen if
1. WBC’s are present along with
2. an overabundance of one type of organism
Sputum of what time of day will represent ‘deeper’ pulmonary secretions?
First morning sputum
How can we induce a cough to get a sputum culture?
1. Induce cough with nebulizers,
2. pulmonary PT,
What do we always need to get with a sputum sample?
Always get a gram stain with the sputum sample
Helpful for directing empiric therapy
IN what kind of disease/bacteria will the sputum contain abundant polymorphonuclear cells and few or no organism will be seen on gram stain?
Atypical pneumonias (mycoplasma and legionella)
Blood culture indications
3. Unexplained post operative shock
4. Unexplained fever of several days duration
Blood culture indications with a pt with chills and fever?
1. Infected burns or UTIs
2. Rapidly progressing tissue infections
3. Postoperative wound sepsis
4. Indwelling venous or arterial catheters
Blood culture indications in debilitated patients receiving what?
Blood cultures used to detect bacteremia and septicemia should mainly be considered in pts with a temp of what?
Standard of care for inpatients with pneumonia prior to starting antibiotics is what?
When and Why would we repeat the culture?
Can repeat in 1 hour or if fever
Two specimens obtained from two separate sites 15 minutes apart in blood cultures. Why do we do this?
How much blood should we draw?
1. # Of organisms per site is low
2. Helps identify contaminants
Total 30-40 ml blood
Blood culture technique?
What can we not draw cultures through?
1. Clean site first with 70% alcohol
3. Follow with Betadine x 2 minutes (follow facility protocol)
3. Wipe bottle tops with alcohol
4. Go to lab immediately
Do not draw blood cultures through central lines or IV’s (contamination)
Which ways can we obtain Urine Cultures?
How much should we collect?
At the very minimum?
What temp should we transport it at?
Is this different for a straight cath?
Is this different for an indwelling cath?
Clean catch, mid void specimen
Collect 5-50ml of urine
4 degress C
Whats the technique for an indwelling catheter?
(how much and at what temp)
1. Disinfect port w/ alcohol
2. Remove 5-10 ml of urine w/ needle and syringe—transfer to sterile container;
3. 4 C
What is the best time to get a uriine sample?
first urination of the day
What do we always send the specimen to the lab as?
ALWAYS Send as UA and urine C and S
Urine dipstick testing
can test what things?
Indicators of possible pyuria
Leukocyte esterase will indicate pyuria if what?
Nitrite will indicate pyuria if what?
If thses are negative but you have positive symptoms what should you do?
-If positive on dipstick likely indicates pyuria
-Indicates the presence of enerobacteriaceae that converts nitrate to nitrite
If negative but + symptoms of UTI still want urine culture
(GET A UA)
What is a Microscopic analysis of urine looking at?
(how do we know if they specimen is contaminated?)
What are the normal values for a microscopic analysis of urine?
Presence of squamous epithelial cells = contamination from genital region
Evaluation of urine sediment from a spun sample
RBC: 0-5 HPF
WBC: 0-5 HPF
Casts: 0-4 hyaline LPF
Lumbar puncture indications
1. Look for blood (possible subarachnoid hemorrhage)
2. Find the organism causing the meningitis or brain abscess
What can we do in the mean time while awaiting lumbar puncture results and why do we do this?
Can do gram stain early on while awaiting culture reports
Cell & chemistry counts will aid in making the diagnosis
When do we want to test Cerebrospinal Fluid (CSF)?
How much should we collect in a lumbar puncture?
At what temp should we transport it at?
What should we do with the lumbar puncture?
1. Suspected meningitis,
2. high fever in infant
Lumbar puncture collect 1-5ml of CSF
Transport at 25 degrees C
Gram stain and Bacterial culture
There is four tubes to fill in a lumbar puncture for CSF. What is in each one?
(1) Cell count,
(2) glucose & protein,
(3) gram stain & culture,
(4) cell count to compare to tube 1
Thoracentesis can be done for two reasons. What are they?
1. Diagnostic and/or therapeutic
-Test the fluid
What are we looking at in the fluid acquired from a thoracentesis?
CEA level (tumor marker), cytology,
When is a Synovial Fluid evaluation done?4
What should not be administered at the same time this is done?
1. Swollen joint
3. inflammation or
4. crystals (gouty arthritis)
Medications should not be administered therapeutically at the same time!
What body fluids might we want to culture?
What would we usually expect to see if we wanted to culture these fluids?
Whats the minimum amount we want to send and at what temp?
Peritoneal, pericardial, pleural, synovial
usually patient has fever or elevated WBCs
Minimum of 1-10cc, send as much fluid as possible
Send at 4 degrees C
What do we swab the cervix for? (if we want to test for what diseases)
Swabs of the urethra or urine testing for what?
Swabs of the cervix for
2. chlamydia as well as other organisms in suspected
3. Pelvic Inflammatory Disease
What should not be done for 24 hours prior to a vaginal/cervical collection?
No douching or tub bathing for 24 hrs prior to collection
What kind of test is good for evaluating vaginitis?
What kind of bacteria are we expecting to be here?
Saline wet mount of vaginal of discharge can show what?
What diseases is this helpful is diagnosing? 2
What do we put on the wet mount?
What organisms can it reveal?
epithelial cells covered with bacteria suggestive of bacterial vaginosis
Can reveal multiple PMN’s
KOH (potassium hydroxide) wet mount can reveal candida organisms
What do we test with in men for gonorrhea and chlamydia and other less common infectious agents ?
Special smaller swabs for urethral sampling
Why do we use urine samples now instead for diagnosis of GC and chlamydia in men?
Urine samples for GC and chlamydia for nucleic acid amplification
Nucleic acid amplification more sensitive then culture
Urethral Culture in men what medium would we use?
Thayer martin/new York media
What pts is a stool sample a routine culture for?
How much should we get at what degree should transport it at?
(for those with prolonged diarrhea or haven't been on antibiotics or hospitalized)
>2 grams; 4 degrees C
Test of choice for those who develop diarrhea on antibiotics or in hospital > 3 days?
How much should we get and at what degree should we transport it at?
C. difficile toxin
> 5 ml; 4 degrees C
What bacteria are we usually looking for with stool culture?
What do we also need to look for/rule out?
Usually look for Staph.,Salmonella, shigella
Also check for ova & parasites