An 8-year-old boy complains of left leg pain for 3 days. On physical examination, his temperature is 38.9degC, and he exhibits irritability when his left leg is moved. A radiograph of the left leg shows changes suggesting acute osteomyelitis in the proximal portion of the left femur. Culture of the infected bone is most likely to grow which of the following organisms?

**Core Concept**
Acute osteomyelitis is a bacterial infection of the bone, commonly caused by Staphylococcus aureus, particularly in children. The infection typically occurs due to hematogenous spread, where bacteria are carried from a distant site to the bone via the bloodstream.

**Why the Correct Answer is Right**
Staphylococcus aureus is the most common cause of acute osteomyelitis in children. This bacterium has a strong affinity for bone tissue and can adhere to the endosteal surface of the bone, leading to infection. The bacteria can enter the bone through the bloodstream, often from a distant site of infection such as the skin or respiratory tract. The proximal femur is a common site for osteomyelitis due to its rich blood supply.

**Why Each Wrong Option is Incorrect**
* **Option A:** Although Pseudomonas aeruginosa can cause osteomyelitis, it is more commonly associated with chronic or nosocomial infections, and less frequently seen in children.
* **Option B:** Escherichia coli is a common cause of urinary tract infections and some cases of osteomyelitis, but it is less likely to cause acute osteomyelitis in children compared to Staphylococcus aureus.
* **Option C:** Klebsiella pneumoniae can cause osteomyelitis, but it is more commonly seen in adults or as part of a polymicrobial infection.

**Clinical Pearl / High-Yield Fact**
Staphylococcus aureus is a common cause of osteomyelitis in children due to its ability to adhere to bone tissue and invade the bone through the bloodstream.

**Correct Answer:** D. Staphylococcus aureus

✓ Correct Answer: D. Staphylococcus aureus