A veterinary doctor had pyrexia of unknown origin. His blood culture in special laboratory media was positive for gram-negative short bacilli which was oxidase positive. Which one of the following is the likely organism grown in culture ?
First, I should recall the common gram-negative, oxidase-positive bacteria. The key here is that it's from a veterinary doctor, so zoonotic pathogens are a possibility. Gram-negative short bacilli might include Pseudomonas, E. coli, but wait, E. coli is oxidase negative. Pseudomonas aeruginosa is oxidase positive and a common opportunistic pathogen. But there's also another possibility: Brucella species. Wait, Brucella is a gram-negative coccobacillus, which is oxidase positive. Brucellosis is a zoonosis that affects veterinarians, especially from handling infected animals. So, Brucella species would fit here. Let me check the characteristics: Brucella is a gram-negative, oxidase-positive, facultative intracellular bacillus. It causes undulant fever, which can present as PUO. Pseudomonas is also oxidase positive but not typically associated with PUO in a vet unless there's a specific exposure. Another possibility is Burkholderia, but that's more in tropical regions. So the most likely answer here is Brucella. The correct answer is probably Brucella abortus, melitensis, or suis. The options might have Brucella as one of the choices. The other options like E. coli, Klebsiella, or Proteus would be oxidase negative, except maybe Pseudomonas. But Brucella is more zoonotic and fits the occupational risk. So the answer should be Brucella species.
**Core Concept**
This question tests knowledge of zoonotic pathogens, particularly **Brucella species**, which are **gram-negative, oxidase-positive, facultative intracellular coccobacilli**. These organisms cause **brucellosis**, a systemic infection with nonspecific symptoms like pyrexia of unknown origin (PUO), especially in high-risk occupations like veterinary medicine.
**Why the Correct Answer is Right**
**Brucella species** (e.g., *Brucella melitensis*, *abortus*, *suis*) are **gram-negative, oxidase-positive, facultative intracellular pathogens**. They are **zoonotic**, transmitted via contact with infected animals or their secretions. Blood cultures may show **short bacilli**, and the organism grows slowly on special media. Brucellosis is a classic cause of **undulant fever** with prolonged fever, malaise, and arthralgia, fitting the clinical scenario of PUO in a veterinary professional.
**Why Each Wrong Option is Incorrect**
**Option A:** *Pseudomonas aeruginosa* is oxidase-positive but not a coccobacillus; it's a **rod-shaped** organism causing opportunistic infections, not typically linked to zoonotic PUO.
**Option B:** *Escherichia coli* is **oxidase-negative**, and while zoonotic, it doesn’t match the morphological or biochemical profile.
**Option C:** *Klebsiella