Virulence, adherence, antigenic diversity

Question 1

Define adhesion and explain the role played by adhesions

Answer 1

Surface protein struction, can be pili or integral outer membrane proteins. These make close contacts

Adherence is a defense against the host’s mechanical cleansing devices

Question 2

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

Answer 2

Each adhesin plays a different role and allows the cells to adapt to changing environment

Different environmental conditions require different adhesions

Some bacteria infect more than one species of host

Question 3

Describe the organization of the pil genes

Answer 3

pilE: expressed gene
pilS: silent cassettes, each cassette is promoterless, incomplete, and oriented in the same direction as the expressed gene

Silent cassettes are introduced into the intact pilE gene as discrete units by recombination (gene conversion or transformation)

Question 4

Describe the manner in which pil gene organization can change

Answer 4

Gene conversion: A silent pilS is copied into expressed pilE site, original pilS locus remains unchanged but pilE locus now expressed a new pilus that is antigenically distinct

Transformation: Cell lyses and releases DNA into the environment, competent cells of same species take up silent cassettes from the donor and recombine them into their own DNA