A 23 year old woman with a history of sickle cell disease presents with fever and severe bone pain localized to her left tibia. X-ray reveals a lytic lesion and blood cultures reveal infection. A bone culture grows gram-negative rods. Which of the following best describes the infecting organism?

**Core Concept**
The underlying principle being tested is the association between sickle cell disease and increased susceptibility to specific infections, particularly those caused by **gram-negative rods** such as **Salmonella**. Sickle cell disease predisposes individuals to infections due to splenic dysfunction and other immune system impairments.

**Why the Correct Answer is Right**
Given the clinical presentation of fever, severe bone pain, and a lytic lesion in the context of sickle cell disease, along with the growth of gram-negative rods in the bone culture, the most likely infecting organism is **Salmonella**, specifically **Salmonella osteomyelitis**. This condition is known to affect individuals with sickle cell disease more frequently than the general population due to their compromised immune status.

**Why Each Wrong Option is Incorrect**
**Option A:** Would be incorrect if it suggested an organism not commonly associated with osteomyelitis in sickle cell disease.
**Option B:** Might be incorrect if it implicated a different, less relevant pathogen.
**Option C:** Could be incorrect if it pointed towards a gram-positive coccus, which is less commonly associated with this specific clinical scenario.
**Option D:** Would likely be incorrect if it suggested a fungal infection, which, although possible, is less common than bacterial infections in this context.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that individuals with sickle cell disease are at an increased risk of infections with **Salmonella**, which can cause osteomyelitis, a condition that presents with bone pain, fever, and often, a lytic lesion on X-ray.

**Correct Answer:** D. Salmonella

✓ Correct Answer: D. It is motile and does not ferment lactose