Bacteria Chapter 10: Intro to Pathogenesis

Question 1

What are the steps bacteria go through to infect human body?

Answer 1

1. bacteria comes in contact with host’s body
2. bacteria adhere to (and transiently colonize) or invade the host
3. bacteria multiply
4. bacteria evade host’s innate immune defence system

Question 2

What does a bacterium require to cause disease?

Answer 2

chemical/molecular mechanisms that damages host (ie. toxins, host-damaging enzymes) or triggers chronic inflammatory response

Question 3

Microorganisms’ Mechanisms of Pathogenesis

Answer 3

1. exposure to pathogen
2. adherence to skin or mucosa
3. invasion through epithelium
4. colonization and growth production of virulence factors
5. a) toxicity: toxin effects are local or systemic
   b) invasiveness: further growth at original and distant sites
6. tissue damage, disease

Question 4

What is bacteremia?

Answer 4

presence of bacteria in blood

Question 5

What is septicaemia?

Answer 5

evidence that bacteria is multiplying in blood

Question 6

What are some virulence factors?

Answer 6

• injectosome
• endotoxin
• anti-phagocytic proteins
• O antigen
• flagellum
• H antigen
• Vi capsule antigen
• cytotoxin
• type I fimbriae
• siderophores
• enterotoxin

Question 7

What does enterotoxin cause?

Answer 7

diarrhea

Question 8

What does endotoxin in LPS layer cause?

Answer 8

fever

Question 9

What does O antigen do?

Answer 9

inhibits phagocyte killing

Question 10

What does H antigen do?

Answer 10

• adherence

- inhibits phagocyte killing

Question 11

What does Vi capsule antigen do?

Answer 11

• inhibits host cell protein synthesis
• Ca2+ efflux from host cell
• adherence

Question 12

What do Koch’s postulates tell us?

Answer 12

determines whether a relationship exists between a particular organism and a disease

Question 13

Have Koch’s postulates been useful?

Answer 13

yes — have been used as a guide to determine the causes of many important diseases, which led to development of treatments for prevention and cure of many infectious diseases

Question 14

What are Koch’s postulates? (4)

Answer 14

1. suspected pathogenic organism should be present in all cases of the disease, and absent from healthy animals
2. pathogenic organism should be isolated from the infected animal(s) and cultivated in pure culture
3. when this culture is inoculated into susceptible (and healthy) animals, it should initiate the characteristic disease symptoms
4. pathogen should be re-isolated from the experimentally infected animals, and shown to be the same as the original pathogen isolated in step 2

Question 15

What are 2 major impediments that can prevent definitive proof of causation using Koch’s postulates?

Answer 15

• certain bacterial pathogens cannot be cultivated in vitro

- sometimes there are no animal models for a specific disease

Question 16

What does the molecular version of Koch’s postulates tell us?

Answer 16

proves that a particular virulence factor or gene is involved in pathogenesis of an organism

Question 17

What are Koch’s molecular postulates?

Answer 17

1. gene(s)/factor should be present in pathogenic strains of the organism, and absent from non-pathogenic strains
2. i) molecular disruption (ie. deletion of gene) should reduce virulence of bacterial strain

OR ii) introducing cloned gene(s) into avirulent strain should render that strain virulent

3. gene(s) must be expressed at some point during the infectious process in experimentally infected animals
4. antibody raised against the virulence factor should offer some protection against infection, in an experimentally infected animal

Question 18

What are some molecule targets that cause disease?

Answer 18

• genes encoding toxins
• pili
• receptors

Question 19

Why are the Molecular Version of Koch’s Postulates important?

Answer 19

although two examples of a bacterium may be from the same species, there may be
significant differences in their DNA that would result in one being a pathogen, and the other not being a pathogen

ie. Streptococcus pneumonia can be a pathogen or non-pathogen – pathogen has genes in its genome that code for enzymes involved in synthesis of a capsule, but non-pathogenic strains don’t

Question 20

Are there any situations where Koch’s postulates may not be applicable?

Answer 20

1st postulate: (pathogen is found only those who are ill)

• there are people that carry pathogenic bacteria as part of their normal flora (carriers) – bacteria do not cause disease to them, but may cause disease in other people if bacteria gets transmitted to them
• bacteria of normal flora can cause disease if they get into a part of the body where they are normally absent