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 compare d prospectively in 29 diabetic patients with limb-threatening foot infectio n, to investigate the effectiveness and reliability of each method, and to evaluate whether any of the two could be more suitable for the microbiologi cal follow-up of severe lesions. Methods Microbiological samples were collected by using both methods at fix ed intervals after therapy commencement (i.e. at day 0, 7, 14, and 30). Sta tistical comparison was performed between the results of each sampling proc edure after the end of follow-up. Results At enrolment, the mean number of isolates per patient was 2.34 by s wabbing and 2.07 by tissue biopsy sampling; the rate of isolation for anaer obes with the two methods was 35% and 25%, respectively; no statistical dif ferences could be observed between the two procedures in terms of either sp ecies or frequency of isolation. Anaerobic species were never detected afte r the first 2 weeks of appropriate treatment, and those ulcers which were s till active at day 30 yielded almost exclusively Gram-positive bacteria. At the end of follow-up, deep tissue cultures appeared to exhibit a higher di agnostic 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 f oot infection. However, our experience seems to suggest that deep tissue mi ght be more sensitive than swabbing for monitoring those isolates that have been selected for antibiotic resistance, i.e. those from ulcers that are s till active after 30 days of treatment.