Microbiology-P D.Essra-L5
1
Genus: Vibrio (comma bacillus)
The genus vibrio comprises members pathogenic to man, others are pathogenic
for animals or insects and many are commensals or saprophytic particularly in
water.
The medically important vibrios:
1. V. cholerae serotype 01, cause cholera
•Biotype Classic
•Biotype El-Tor
2. V. cholerae serotype 0139 bengal, cause cholera
3. V. cholerae serotype non-01, cause cholera-like diarrhea and rarely extra-
intestinal infections
4. V. parahaemolyticus, cause gastroenteritis.
Microscopical appearance:
•Gram -ve, non-sporing, non-capsulated.
•Small rods, slightly curved (comma shaped). Often lose their curved
appearance on artificial cultivation.
•Actively motile by a single polar flagellum.
Cultural characteristics:
Aerobic
Grows on ordinary media.
Grows best in an alkaline pH (8.5-9.5).
On agar media colonies are convex, smooth, round, and opaque.
On MacConkey agar colonies are colorless (late lactose fermenter).
Microbiology-P D.Essra-L5
2
On TCBS (Thiosulfate-citrate-bile-sucrose) agar a selective and differential
medium for the genus Vibrio.
V. cholerae colonies are large and yellow due to sucrose fermentation.
V. parahaemolyticus grows on TCBS without fermenting sucrose. Thus
the color of the colonies remain green.
Biochemical reactions:
Oxidase +ve
Catalase +ve
Indole +ve
Voges-proskauer test:V. cholerae biotype Classical –ve, V. cholerae biotype
El-Tor +ve
Growth in broth containing 8%NaCl:V.cholerae–ve, V. parahaemolyticus +ve
(halophile)