Cholerae

1. Describe the general properties of Vibrionaeceae.

2. What are main genre of Vibrionaeceae.

3. How would you go about identifying this family of enteric gram negative rods?

4. Discuss the pathogenesis, treatment, prophylaxis of V.Cholerae.

5. V. parahaemolyticus and V Alginolyticus are also part of Vibrio genus. What do they cause?

Vibrionaeceae are the 2^nd most important group of gram negative enteric rods. They are gram –ve, oxidase +ve, facultative anaerobes & have a single polar flagellum. Some of the major genre include: Vibrio, Camplobacter, Helicobacter, Aeromonas and Plesiomonas. The diagnosis/identification process is similar to those of Enterbacteriaceae. There are four main process: Enrichment medium (alkaline peptone H₂O – ph 8.4), Selective medium (i.e.: two types  Monsours medium (ph 8.5-9.2) – looking for gelatin liquefaction colonies  2^nd type is TCBS medium (ph 8.6) – looking for large yellow sucrose fermenting colonies), slide agglutination tests (i.e.: see if there is any agglutination of pathogen with selective antibody), specific biochemical tests (Remember: DICKMMUV).

V.Cholerae has two main biotypes: Classical and El Tor. It is also subdivided into three serological subgroups (Ogawa, Inaba, Hikojima). It is transmitted by the faecal oral route – due to contaminated food, water, or seafood (marine life). The pathogenesis is due to bacteria multiplying in the intestines. It has a pilus – therefore able to attach to intestinal epithelial cells. Adhesion causes release of potent exotoxin – called choleragen. This toxin is made up of two subunits: A & B, and it is the A subunit that causes the leak of Na⁺ / Cl ^- / HCO₃-/ K⁺ / fluid into the intestinal lumen  hence causes severe dehydration (i.e: stimulates adenylate cyclase -> stimulate cAMP production ->stimulate all ionic / fluid losses). About 1 L of fluid is lost in 1 hour and death can occur within 3-4 hours after infection. The carrier rate is 3 weeks. Treatment is by rehydrating the person and achieving electrolyte balance. Tetracycline is given to eliminate the residual bacteria and toxins. Prophylaxis: Vaccines are not so effective – although it can offer some protection. There is a heat killed vaccine (O1, inaba and ogawa serotypes), oral vaccines also help protect. V.Cholerae of non-01 type causes diarrhoea and dysentery. Recently pandaemics (1993) are caused by V.Cholerae O139.

V. Parahaemolyticus

1. What is V . Parahaemolyticus, describe its pathogenesis.

2. What is V. alginolyticus, what does it cause?

V. parahemolyticus is another species of the vibrio genus. It causes watery diarrheao / dysentery as a result of seafood poisoning. Major cause of dysentery in Japan (uncooked sushi). This occurs due to ingestion un cooked marine life leading to gastroenteritis. Its pathogenesis involves adhesion, by pili, release of toxin, invasion of epithelial cells by this toxin, and formation of lateral flagella.

Similarly, V. alginolyticus is another species part of the vibrio genus. It causes wound infections, and inflammation of the external ear (external otitis).

Category: Microbiology Notes