Host-microbe interactions

Question 1

define human host

Answer 1

• provides favourable environment for growth of many organisms

Question 2

Why is growth optimal in human host?

Answer 2

• high nutrients
• protection from UV exposure
• pH varies (neutral in colon)
• consistent temp
• lots of oxygen
• moist

Question 3

What are the different pHs in the body?

Answer 3

• stomach: 2-4
• intestine: 4-6
• colon: 7

Question 4

Where in the human body do higher populations of microorganisms exist?

Answer 4

• regions more continuously exposed to external environment

Question 5

What provides the initial site of contact?

Answer 5

• mucous membranes

Question 6

What does saliva do?

Answer 6

• lysozyme attacks cell wall

Question 7

What are mucous membranes needed for?

Answer 7

• cell protection and nutrition transfer in tissue layers
• lysozymes keep things under control

Question 8

What parts of the body need to be sterile?

Answer 8

eyes and organs

Question 9

What is flora?

Answer 9

• microorganisms that establish more or less permanent residence that DO NOT cause disease under NORMAL conditions

Question 10

What causes disease from flora?

Answer 10

• overabundance of bacteria

Question 11

What is transient microbiota? where would you find it?

Answer 11

• microorganisms present for several days/weeks/months then disappear
• hospital

Question 12

What is the condition for a fetus in the womb vs vaginal birth? what about C section?

Answer 12

• sterile in womb
• bacteria as soon as it exits vagina
• no bacteria for C section but as soon as they feed

Question 13

What is a pathogen?

Answer 13

• microorganism that causes damage to host (disease)

Question 14

What is an infection?

Answer 14

• invasion/colonization of body by pathogenic microorganisms

Question 15

What is disease?

Answer 15

• infection causes change in state of health (damage/injury to host impairing function)

Question 16

What is the difference between pathogen and disease

Answer 16

• pathogen causes damage to host

Question 17

What is pathogenicity?

Answer 17

• ability of pathogen to cause damage to host (cause disease) by overcoming host defences

Question 18

What is an opportunistic pathogen?

Answer 18

• certain amount of opportunity required
  -ex. salmonella must have certain amount to cause food poisoning

Question 19

What is a strict pathogen?

Answer 19

• will always cause disease, just must be exposed to host

Question 20

What is virulence? give an example

Answer 20

• measure of degree of pathogenicity
  -ex. salmonella —> needed in thousands, shigella –> 100s

Question 21

What is commensalism

Answer 21

• type of symbiosis (living together) where one organism benefits and the other is unaffected (+, neutral)

Question 22

What is mutualism?

Answer 22

• both organisms benefit (+ +)

Question 23

What is parasitism?

Answer 23

• one organism benefits at expense of other (+, -)

Question 24

What is microbial antagonism?

Answer 24

• competition among microbes where members of normal pop provide competition for potential invading pathogens = protect host

Question 25

What is conjuctiva?

Answer 25

- membrane around eyes/gums (sterile)

Question 26

Opportunistic microorganisms ___ ____ cause disease in normal habitat in healthy person, but may in ____ _____.

Answer 26

- do not - different environment

Question 27

Give an example of when opportunistic bacteria are healthy vs problematic

Answer 27

- healthy in GI, cause problems in vaginal tract

Question 28

What does the outcome of host-microbe relationship depend on?

Answer 28

- pathogenicity of the microorganism - host condition (resistance/susceptibility)

Question 29

What are the 4 rules for the application of Koch's postulates?

Answer 29

- same pathogen must be present in every case of disease - pathogen must be isolated from diseased host and grown in pure culture - pathogen from pure culture must cause disease when inoculated to healthy lab animal - pathogen must be isolated from inoculated animal and shown to the original organism

Question 30

Simplify the application of Koch's postualtes

Answer 30

- pulled out of host, make pure culture, must get same response from healthy organism

Question 31

Not everything is culturable, why?

Answer 31

- can't replicate the environment

Question 32

What is the problem with Koch's postulates?

Answer 32

- some microorganisms can cause more than 1 disease - some hosts obtain more than 1 disease from pathogen