Microbial Pathogenesis

Question 1

What are the two major mechanisms by which bacteria cause disease?

Answer 1

1. Toxin production

2. Invasion and Inflammation

Question 2

What are the two types of toxins bacteria produce? What is the difference btwn them?

Answer 2

Endotoxins and Exotoxins

1. Exotoxins are polypeptides released by the cell; can be G+ or G-
2. Endotoxins are lipopolysaccharides (LPS) that form part of the membrane– only in G- rods and cocci– these are NOT released from the cell. Cause fever and shock

Question 3

Explain Invasion and Inflammation in the context of bacteria causing disease.

Answer 3

Invasion is when large numbers of bacteria grow locally and induce an inflammatory response–erythema, edema, warmth, pain

Invasion usually happens first and then inflammation follows

Question 4

List the (7) stages of infection:

Also, what are the 3 major routes of spread?

Answer 4

1. Transmission from an external source to a portal of entry
2. Evasion of primary host defenses such as skin or stomach acid
3. Adherence to mucous membranes via bacterial pili
4. Colonization by growth of bacteria at the site of adherence

(1-4 = incubation period)

5. Disease symptoms caused by toxins or invasion –> inflammation
6. Host response (specific and non-specific)
7. Progression or resolution of disease

**Spread: blood, lymph, CSF are major routes

Question 5

What is vertical transmission?

Answer 5

Microbes that are transmitted from mother to offspring

Question 6

What are the 3 types of vertical transmission?

Answer 6

1. across the placenta
2. in the birth canal
3. breastmilk

Question 7

What is horizontal transmission?

Answer 7

Person to person transmission

Question 8

What are the 4 major portals of entry?

Answer 8

1. Skin
2. Respiratory
3. GI tract
4. Genital tract

Question 9

There are several non-toxin virulence factors, like enzymes, that are secreted by bacteria to bring about pathogenesis. Name the 4 most prominent:

Answer 9

1. Collagenase and Hyaluronidase
2. Coagulase
3. IgA Protease
4. Leukocidins

Question 10

What do Collagenase and Hyaluronidase do as non-toxin virulence enzymes?

Answer 10

Degrade collagen/hyaluronic acid. Enables bacteria to get through subQ tissue
**important in cellulitis causes by strep pyogenes

Question 11

What does coagulase do as a non-toxin virulence enzyme? What produces it? How does it benefit the bacteria?

Answer 11

Produced by Staph Aureus. Accelerates formation of fibrin clot from fibrinogen (clot can protect bacteria from phagocytosis by walling off infected area)

Question 12

What does IgA protease do as a non-toxin virulence enzyme?

Answer 12

Degrades IgA. Enables bacteria to bind to mucous membranes (produced by N. Gonorrhea, haemophilus influenza, strep pneumo)

Question 13

What do Leukocidins do as non-toxic virulence enzymes?

Answer 13

Destroy both neutrophilic lymphocytes and macrophages