Microbiological evaluation of resection margins of the infected diabetic foot ulcer

Abstract

To evaluate the impact of surgical debridement on the microbiology of resection margins of an infected diabetic foot ulcer and to compare the use of marginal sampling as a guide for antimicrobial therapy. Forty consecutive participants were studied. Tissue samples from infected diabetic foot ulcers were obtained at first contact by podiatrists. After surgical debridement to macroscopically healthy tissue, multiple samples were obtained from the margins of the residuum and also from excised non-viable tissue. Debridement was done by a single surgeon. Bacterial species were classified according to pathogenic potential a priori into Red Group-Definite pathogen causing infection, Yellow Group-Likely to be causing infection if present in more than one specimen and Green Group -Commensals, not causing infection. There was a relative reduction of 49% (p=0.002) in bacteria in the most pathogenic (red) group, and 59% (p=0.002) in the yellow group in podiatry samples compared with resection specimen. Positive cultures from margins of the residuum were observed in 75% of cases. There was a relative reduction of 67% (p=0.0001) in bacteria in the red and 48% (p=0.06) in the yellow group in marginal samples from the residuum compared with podiatry samples. After surgical debridement to healthy tissue, positive cultures from marginal tissue samples provided vital information on the presence of pathogenic bacteria. This allowed antibiotics to be individualised post-surgical debridement.