A patient develops septicemia after consuming raw oysters. The organism is oxidase positive with pink colonies on MacConkey and is susceptible to O/129. Which organism is most likely?

A patient develops septicemia after consuming raw oysters. The organism is oxidase positive with pink colonies on MacConkey and is susceptible to O/129. Which organism is most likely?

• A. Aeromonas hydrophila
• B. Pseudomonas putida
• C. Serratia marcescens
• D. Vibrio vulnificus

Answer: (D)

Infections from raw seafood, especially oysters, are classic for Vibrio species. Vibrio vulnificus is particularly notorious for causing septicemia after ingesting contaminated shellfish, and it is an oxidase-positive, curved Gram-negative rod that responds to vibriostatic testing with O/129. The combination described—oxidase positive, a MacConkey appearance described as pink colonies, and susceptibility to O/129—fits the lab profile used to identify vibrios and points to Vibrio vulnificus as the most likely organism in this clinical scenario. Other organisms listed can be oxidase-positive, but they do not fit the typical oyster-associated septicemia pattern or the O/129 susceptibility clue. Aeromonas hydrophila can cause gastroenteritis or wound infections but is less characteristically linked to oyster septicemia; Pseudomonas putida is an environmental organism and not the classic seafood-associated pathogen in this context; Serratia marcescens is more commonly a nosocomial pathogen and does not align with the oyster-sepsis scenario.

Infections from raw seafood, especially oysters, are classic for Vibrio species. Vibrio vulnificus is particularly notorious for causing septicemia after ingesting contaminated shellfish, and it is an oxidase-positive, curved Gram-negative rod that responds to vibriostatic testing with O/129. The combination described—oxidase positive, a MacConkey appearance described as pink colonies, and susceptibility to O/129—fits the lab profile used to identify vibrios and points to Vibrio vulnificus as the most likely organism in this clinical scenario.

Other organisms listed can be oxidase-positive, but they do not fit the typical oyster-associated septicemia pattern or the O/129 susceptibility clue. Aeromonas hydrophila can cause gastroenteritis or wound infections but is less characteristically linked to oyster septicemia; Pseudomonas putida is an environmental organism and not the classic seafood-associated pathogen in this context; Serratia marcescens is more commonly a nosocomial pathogen and does not align with the oyster-sepsis scenario.