A 35 year old patient presents with sudden watery diarrhea and severe dehydration. A stool sample is cultured. Gram stain shows comma-shaped Gram-negative rods; Thiosulfate citrate bile salt agar yields yellow colonies; oxidase is positive; motility is present; TSI shows A/A with no black precipitate; nitrate reduces to nitrite before zinc. Which organism do you suspect?

Prepare for the CAMLPR Microbiology Test. Utilize flashcards and engaging multiple-choice questions, each equipped with descriptions and explanations. Ready yourself for an excellent performance!

A key idea here is recognizing Vibrio cholerae by combining its distinctive lab features with the clinical picture of cholera. The organism is a curved, Gram-negative rod that is oxidase-positive and motile, fitting the Vibrio group. On thiosulfate citrate bile salt agar (TCBS), Vibrio cholerae forms yellow colonies because it ferments sucrose; this differentiates it from other vibrios such as those that produce green colonies when they don’t ferment sucrose. The triple-sugar iron test showing an A/A (acid/acid) result with no black precipitate means there’s acid production from carbohydrate fermentation without hydrogen sulfide, which is consistent with Vibrio and helps distinguish it from organisms that produce H2S. Nitrate reduction to nitrite (before zinc is added) indicates active nitrate reductase, a trait seen in Vibrio species. Clinically, the profuse watery “rice-water” diarrhea caused by cholera toxin matches Vibrio cholerae, reinforcing the identification.