Microbial profile and utility of soft tissue, pus, and bone cultures in diagnosing diabetic foot infections.

OBJECTIVE: This study assessed the utility of pus, soft tissue, and bone specimens in diagnosing diabetic foot infections and the spectrum of the microbial flora and in vitro susceptibility to antibiotics.

SUBJECTS AND METHODS: This prospective study was carried out in 60 consecutive patients with diabetes having clinically infected foot ulcers. Detailed history, physical examination, and investigation were carried out to diagnose the presence of osteomyelitis and the microbial etiology of foot ulcers. Foot ulcers were classified as per Wagner's classification. Soft tissue, pus, and bone samples were obtained and cultured for aerobic and anaerobic bacteria, and antimicrobial susceptibility testing was carried out as per the standard protocol.

RESULTS: Causative bacteria were isolated in 55 of 60 patients, and 157 isolates were cultured from 117 specimens with an average of 1.34 isolates per cases; however, the number of isolates per specimen did not differ among the various types of samples (P=0.78). Pus and soft tissue had predominantly polymicrobial flora, whereas bone infections were monomicrobial. The isolates from soft tissue specimens were different from those from bone and pus in 57% and 54% of cases, respectively. The common bacterial isolates from 117 specimens included Escherichia coli (21%) and Proteus species (15.9%). Nearly 70% of Staphylococcus aureus isolates were methicillin sensitive. All S. aureus and Enterococcus isolates were sensitive to vancomycin. Susceptibility of Gram-negative organisms to ciprofloxacin was 50%.

CONCLUSIONS: Diabetic foot infections are mostly polymicrobial with Gram-negative predominance. Multiple sampling from superficial and deep tissues, including bone, when involved, yields more relevant information diagnostically and therapeutically.