1. Virulence, Adherence,
& Antigenic Diversity

2. INITIAL PATHOGEN-HOST INTERACTIONS
Host must make contact with its environment
exchange air
ingest food
eliminate waste
HOST DILEMMA
PREVENTION OF MICROBIAL ENTRY VS
CONTACT WITH ENVIRONMENT

3. PATHOGENS CAPITALIZE ON POINTS OF ENTRY
DIGESTIVE TRACT
RESPIRATORY TRACT
UROGENITAL TRACT
CONJUNCTIVA
HOST POSSESSES DEFENSE MECHANISMS
TO PREVENT ENTRY
MECHANICAL CLEANSING
e.g. blinking & peristalsis

4. pilC pilE opa capsule opc Adherence Adherence Invasion
Serum resistance
Adherence
Invasion

5. a bacterial defense against host’s mechanical cleansing
ADHERENCE
a bacterial defense against host’s mechanical cleansing
HOST CELL
RECEPTOR
bacterium
BACTERIAL
ADHESIN
PILI
OMPs
host cell
requires two factors
host receptor
bacterial adhesin

6. surface protein structure
ADHESIN
surface protein structure
1) pilus (fimbria) - for attachment at a distance
2) non-fimbrial adhesin
(outer membrane protein) - for intimate attachment

7. pili
flagella

8. ADHESIN DIVERSITY HOST RANGE ENVIRONMENTAL CONDITIONS
SPECIFIC ADHESIN FOR SPECIFIC HOST RECEPTOR
ex. N. GONORRHEA (VAGINA vs RECTUM)
ENVIRONMENTAL CONDITIONS
ex. Uropathogenic E. COLI (PYELONEPHRITIS ISOLATES)
EXPRESS
TYPE 1 PILI – (Bladder) LIQUID
TYPE P PILI – (Kidney) SOLID SURFACE

9. VARYING ADHESIN COMPOSITION
ADHESIN DIVERSITY
MEDICAL IMPORTANCE
NEISSERIA GONORRHEA
AVOID
IMMUNE SYSTEM BY
VARYING ADHESIN COMPOSITION

10. Majority with one antigen
Minority with different antigen

11. majority killed
by immune response
subpopulation avoids
immune response

12. Subpopulation multiplies
New subpopulation

13. ANTIGENIC VARIATION

14. MECHANISMS OF ANTIGENIC VARIATION
each N. gonorrhea cell
possesses genetic information
for a large number of variant pilin proteins
thus, each cell can produce progeny
that synthesize pili
that exhibit different epitopes
than did its parent

15. } PILIN GENE ORGANIZATION pilE pilS pilE - expressed due to promoter
pilS - silent genes due to
i) lack of promoter
ii) incomplete
pilS genes same orientation as pilE } A B C A
promoter
pilE
pilS

16. upon the sequence of pilE
Antigenicity depends
upon the sequence of pilE } A A B C A }
pilS
pilE B A B C B

17. MECHANISMS
i) gene conversion
ii) transformation

18. Gene Conversion pilS = endogenote A B C A type A pilus A B C
type B pilus
recombination

19. Transformation Lysed Donor Recipient pilS = exogenote B A C
recombination A B C C
Recipient
type C pilus

20. Antigenic possibilities are infiniteD X X B
B/C
B/C
B/C/D