A veterinary doctor had pyrexia of unknown origin. His blood culture in special laboratory media was positive for gram-negative sho bacilli which was oxidase positive. Which one of the following is the likely organism grown in culture ?
## Core Concept
The question involves identifying a gram-negative short bacillus that is oxidase-positive, isolated from a blood culture. This scenario suggests a zoonotic infection, which is an infection that can be transmitted from animals to humans. The key details here are the gram-negative short bacillus morphology and the oxidase-positive characteristic.
## Why the Correct Answer is Right
The likely organism in this scenario is *Francisella tularensis*, which is a gram-negative short bacillus. It is known to cause tularemia, a zoonotic disease that can be contracted through contact with infected animals or contaminated water. *Francisella tularensis* requires special media for growth, such as chocolate agar or Francisella tularensis media, and is oxidase-positive. This matches the description provided in the question.
## Why Each Wrong Option is Incorrect
* **Option A:** This option is not provided, but typically, incorrect options might include bacteria like *Pasteurella multocida*, which is also zoonotic but usually associated with animal bites and has different growth requirements.
* **Option B:** Similarly, without the specific organism listed, one might consider *Burkholderia pseudomallei*, which causes melioidosis. While it is a gram-negative bacillus, it doesn't fit as well with the description of being a short bacillus and having the specific characteristics mentioned.
* **Option D:** This could potentially include *Yersinia pestis*, the causative agent of plague. However, *Yersinia pestis* is typically described as having a characteristic bipolar staining pattern and is not as commonly associated with the specific laboratory growth requirements and clinical presentation described.
## Clinical Pearl / High-Yield Fact
A key point to remember is that *Francisella tularensis* is a highly infectious agent that can cause severe disease in humans, known as tularemia. It is often associated with exposure to infected rabbits or other small mammals. Laboratory diagnosis can be challenging due to its fastidious growth requirements.
## Correct Answer Line
**Correct Answer: C. Francisella tularensis.**