Chapter 16: Host-Microbe Interactions: Establishing Cause of Disease

Question 1

In general, how can Koch’s postulates establish the cause of disease? (2)

Answer 1

• based on the germ theory of disease
• allows determination of specific microorganism that causes disease

Question 2

what are the four rules of Koch’s Postulates that establish the cause of disease?

Answer 2

1. The same pathogen should be present in every case of the disease
2. the pathogen must be isolated and grown in pure culture
3. Pathogen from the pure culture should cause disease when inoculated into a healthy lab animal
4. The same microbe should be isolated again from the inoculated individual

Question 3

What are the exceptions to Koch’s Postulates?

Answer 3

1. Some bacteria will not grow in pure culture
2. Some pathogens cannot be used to infect lab animals
3. Sometimes several different microorganisms can cause the same disease
4. Sometimes one pathogen can cause many different diseases

Question 4

Why is Treponema pallidum an exception to Koch’s Postulates?

Answer 4

• causative agent of syphilis
• will not grow in pure culture

Question 5

Why is HIV an exception to Koch’s Postulates?

Answer 5

will not infect lab animals

Question 6

Why is Pneumonia an exception to Koch’s Postulates?

Answer 6

Several different microorganisms can cause this

Question 7

Why is S. pyogenes an exception to Koch’s Postulates?

Answer 7

It can cause many different diseases
ie. strep throat, skin infections, scarlet fever

Question 8

What are the different mechanisms of pathogenesis? aka establishing infection? (2)

Answer 8

• adherence
• invasiveness

Question 9

What occurs in adherence?

Answer 9

• surface molecules called adhesins allow a pathogen to attach
• often sticks to specific receptors on host cell surface

Question 10

What are some examples of adherence?

Answer 10

• bacterial capsules, pili, and fimbriae
• viral spikes

Question 11

Study this diagram of adherence with hemagglutinin and neuraminidase

Answer 11

HA - here I come
NA - need to get out

Question 12

What is invasiveness?

Answer 12

• ability of a pathogen to invade and multiply in tissues

Question 13

What two types of molecules promote invasiveness?

Answer 13

• extracellular enzymes called exoenzymes
• invasin

Question 14

What are exoenzymes?

Answer 14

• degrade or alter host cells and tissues

Question 15

Name the 3 exoenzymes

Answer 15

• fibronolysin
• collagenase
• coagulase

Question 16

What is the function of fibronolysin?

Answer 16

• degrades fibrin clots (S. pyogenes)

Question 17

What is the function of Collagenase?

Answer 17

• degrades connective tissue (vibro and clostridium do it)

Question 18

What is the function of coagulase?

Answer 18

• promote blood clots around the bacterial cell (staphylococci)

Question 19

What is invasin?

Answer 19

• surface proteins that cause rearrangement of host cell cytoskeleton

Question 20

What does invasin do?

Answer 20

• forces host cell to take in the bacterium

Question 21

How is salmonella enterica an example of invasin?

Answer 21

• forces “ruffling” by intestinal cells