Deep tissue biopsy vs. superficial swab culture monitoring in the microbiological assessment of limb-threatening diabetic foot infection

Aims The results of ulcer swabbing vs. deep tissue biopsy have been compared prospectively in 29 diabetic patients with limb-threatening foot infection, to investigate the effectiveness and reliability of each method, and to evaluate whether any of the two could be more suitable for the microbiological follow-up of severe lesions. Methods Microbiological samples were collected by using both methods at fixed intervals after therapy commencement (i.e. at day 0, 7, 14, and 30). Statistical comparison was performed between the results of each sampling procedure after the end of follow-up. Results At enrolment, the mean number of isolates per patient was 2.34 by swabbing and 2.07 by tissue biopsy sampling; the rate of isolation for anaerobes with the two methods was 35% and 25%, respectively; no statistical differences could be observed between the two procedures in terms of either species or frequency of isolation. Anaerobic species were never detected after the first 2 weeks of appropriate treatment, and those ulcers which were still active at day 30 yielded almost exclusively Gram-positive bacteria. At the end of follow-up, deep tissue cultures appeared to exhibit a higher diagnostic sensitivity with respect to swabs. Conclusions Swabbing and deep tissue cultures appear to be equally reliable for the initial monitoring of antimicrobial treatment in severe diabetic foot infection. However, our experience seems to suggest that deep tissue might be more sensitive than swabbing for monitoring those isolates that have been selected for antibiotic resistance, i.e. those from ulcers that are still active after 30 days of treatment.