L23 virulence, adherence, and antigenic diversity Flashcards
benefit of adherence
protects from the hosts mechanical cleansing devices
helps escape from immune response
requirements of adherence
- a host cell surface receptor(usually a specific carbohydrate residue)
- a bacterial adhesin (usually a surface protein structure) can be a pili or integral outer membrane proteins
bacteria may be able to make many different adhesins for
different types of hosts
different environments
to evade the immune system
N. Gonorrhea adhesins
randomly change the appearance of their pili and non-fimbrial proteins.
1st pili are used to adhere to epithelial cells, then the immune system recognizes that pili and kills all of those cells but in the meantime a subpopulation has changed the pili that they are expressing (antigenic variation) and exscape the immune system and the process repeats
antigenic variation
being able to express many different forms of an antigenic protein.
a single cell has genes for many different pilin proteins
pilE
expressed pilin gene
pilS
silent pilin cassettes (genes)
lack a promoter
are incomplete
oriented in the same direction as the expressed gene
2 mechanisms which allow pilS genes to be introduced into the pilE gene location
gene conversion
transformation
gene conversion
a silent pilS cassette is copied into the expressed pilE site. the original pilS remains unchanged. the pilE locus now expresses anew pilus that is antigenically distinct from the old pilus
gene transformation
piliated gonococci lyse easily releasing DNA into the environment. they are also naturally competent for NDA transformation. therefore the silent cassettes can come from outside the cell as a result of transformation
adhesin diversity
many bacterial species possess a variety of adhesins that each play a different role. this diversity allows for cells to adapt to changing environments such as different hosts or conditions
