Vibrio cholerae

It is the causative agent of cholera. Cholera is mainly seen in developing countries and may cause outbreaks linked to improper sanitation. In the United States, a few sporadic cases have been reported after 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

Cholera toxin is an exotoxin that causes ADP ribosylation and activation of Gs. This activates adenylate cyclase and increases cAMP. Clinically, 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 findings:
  • 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 O1 or non-O1 antisera can be done for epidemiological purposes.