Vibrio cholerae

It is the causative agent of cholera. It is a disease mainly seen in developing countries that may cause outbreaks linked to improper sanitation. In the United States, a few sporadic cases have been reported caused by the consumption of raw shellfish. There are many serogroups of V. cholerae, but only two – O1 and O139 – cause outbreaks. V. cholerae O1 has caused all recent outbreaks

Human pathology

The cholera toxin is an exotoxin that causes ADP ribosylation and activation of Gs, thus activating adenylate cyclase and increasing cAMP. It presents as watery diarrhea called “rice water stools.” If untreated, severe electrolyte imbalances and dehydration can occur.

Laboratory diagnosis of cholera

Stool samples and rectal swabs are collected. Hanging drop preparation shows darting motility. Gram stain shows curved Gram negative bacilli. No pus cells or RBCs are seen in stool samples. Culture on blood agar shows a greenish zone around the colonies, which slowly clears out. Mac Conkey’s agar shows late lactose fermenting colonies. TCBS (thiosulfate, citrate, bile, sucrose) agar shows yellow colonies. It is oxidase positive. Serotyping with O 1 or non O1 antisera can be done for epidemiological purposes.