Virulence, Adherence, & Antigenic Diversity

Question 1

Define adherence.

Answer 1

Adherence requires 2 factors:

1. host cell surface receptor, typically a specific carbohydrate residue
2. bacterial adhesin - surface protein, either pili (polymer of pilin proteins) or transmembrane.

Question 2

Describe how adhesion diversity permits pathogens to escape host immune response.

Answer 2

• each adhesin plays a different role, allowing it to adapt to several different environments
• can generate adhesins specific to a host
• specific adhesin for specific environment

EVADING THE HOST
- by changing the adhesin after the host immune system has classified the original adhesin as an antigen => evades detection with new adhesin

Question 3

Describe the organization of the pil genes.

Answer 3

2 types

• pilE = expressed
• pilS = silent = no promoter, incomplete, oriented in same direction as expressed pil gene

Question 4

Describe the manner in which pil gene organization can change.

Answer 4

• pilS genes are introduced into intact pilE gene as discrete units
• gene conversion: one of the pilS cassettes is copied and pasted into the pilE locus (pilS remains the same, but pilE now expresses a different pili)
• transformation: competent N. gonorrhea cells take up pilS DNA from the environment (from lysed gonorrhea cells) and recombine them into the pilE locus

Question 5

Name and describe the process by which N. gonorrhea can avoid immune surveillance.

Answer 5

1. uses one type of adhesin for adherence and entry
2. host immune system detects pili as antigen and begins killing some bacteria
3. subpopulation undergo antigenic variation to change shape and composition of their pili => avoids detection