Pathogens isolated from deep soft tissue and bone in patients with diabetic foot infections

We sought to determine the similarity of pathogens isolated from soft tissue and bone in patients with diabetic foot infections. It is widely believed that soft-tissue cultures are adequate in the determination of causative bacteria in patients with diabetic foot osteomyelitis. The culture results of specimens taken concurrently from soft-tissue and bone infections show that the former does not predict the latter with sufficient reliability. We sought to determine the similarity of pathogens isolated from soft tissue and bone in patients with diabetic foot infections.

Forty-five patients with diabetic foot infections were enrolled in the study. Patients had to have clinically suspected foot lesions of grade 3 or higher on the Wagner classification system. In patients with clinically suspected osteomyelitis, magnetic resonance imaging, scintigraphy, or histopathologic examination were performed. Bone and deep soft tissue specimens were obtained from all patients by open surgical procedures under aseptic conditions during debridement or amputation. The specimens were compared only with the other specimens taken from the same patients.

The results of bone and soft-tissue cultures were identical in 49% (n = 22) of cases. In 11% (n = 5) of cases there were no common pathogens. In 29% (n = 13) of cases there were more pathogens in the soft-tissue specimens; these microorganisms included microbes isolated from bone cultures. In four patients (9%) with culture-positive soft-tissue specimens, bone culture specimens remained sterile. In one patient (2%) with culture-positive bone specimen, soft-tissue specimen remained sterile.

Culture specimens should be obtained from both the bone and the overlying deep soft tissue in patients with suspected osteomyelitis whose clinical conditions are suitable. The decision to administer antibiotic therapy should depend on these results.