A 45-year-old man with liver cirrhosis develops explosive watery diarrhoea followed by hypotension 12 hours after eating raw oysters at a coastal restaurant. Blood cultures eventually grow a curved gram-negative rod that is halophilic, oxidase-positive and grows on TCBS agar as a yellow colony. What organism is responsible and what explains the particularly high mortality in cirrhotic patients?

• A Vibrio vulnificus — the organism thrives on excess iron in cirrhosis; it causes primary septicaemia with mortality >50% in cirrhotic/iron-overloaded patients ✓
• B Vibrio cholerae — liver disease impairs mucosal defence; mortality same as immunocompetent
• C Vibrio parahaemolyticus — yellow TCBS colonies indicate urease-positive strains more virulent in liver disease
• D Aeromonas hydrophila — produces haemolysin that is hepatotoxic in cirrhosis

Explanation

Vibrio vulnificus (yellow colonies on TCBS agar due to sucrose fermentation, unlike V. parahaemolyticus which is green/blue) is a halophilic marine vibrio causing raw shellfish-associated primary septicaemia, especially dangerous in patients with liver disease, haemochromatosis or immunosuppression. Cirrhotic livers have impaired transferrin iron-binding, leaving excess free serum iron which promotes explosive V. vulnificus bacteraemia. Mortality in underlying liver disease exceeds 50%. V. parahaemolyticus causes diarrhoea but not primary septicaemia; its colonies on TCBS are blue-green (Kanagawa phenomenon positive strains).

Reference: Ananthanarayan & Paniker's Textbook of Microbiology, 11th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.