**Core Concept**
The gold standard diagnostic method for guiding antibiotic therapy in osteomyelitis involves identifying the causative microorganism(s) responsible for the infection. This requires a microbiological test that can accurately isolate and culture the pathogen from a bone sample.

**Why the Correct Answer is Right**
Bone biopsy and culture is the definitive diagnostic method for osteomyelitis, allowing for the direct isolation of the causative microorganism from the affected bone tissue. This method is particularly useful in cases where blood cultures are negative or when the patient has received prior antibiotic therapy. The bone biopsy sample is typically obtained using a trephine needle or a surgical incision, and the tissue is then sent for microbiological analysis, including culture, Gram stain, and antibiotic susceptibility testing.

**Why Each Wrong Option is Incorrect**
**Option A:** Blood cultures alone may not be sufficient to diagnose osteomyelitis, as the causative microorganism may not be present in the bloodstream.
**Option B:** Imaging studies such as X-rays, CT scans, or MRI can help identify bone lesions and inflammation, but they cannot provide a definitive diagnosis of the underlying infection.
**Option C:** Histopathological examination of bone tissue can provide information on the presence of inflammation and infection, but it may not be sufficient to identify the specific causative microorganism.

**Clinical Pearl / High-Yield Fact**
Bone biopsy and culture should be considered in cases of osteomyelitis where blood cultures are negative or when the patient has received prior antibiotic therapy. This can help guide targeted antibiotic therapy and improve patient outcomes.

**Correct Answer: C. Bone biopsy and culture**