Comparison of Microbiological Results of Superficial Swab versus Deep Tissue Biopsy in Diabetic Foot Infections: A Prospective Observational Study from North India

Abstract

Introduction: Diabetes mellitus is the leading cause of nontraumatic lower extremity amputation worldwide. Risk of developing a foot ulcer in diabetic patients has increased to 12-25% during their lifetime. Inappropriate sampling technique leading to contaminated samples is a well-known threat among patients of diabetic foot. In this study we compared two microbiological sampling techniques, superficial swabbing and deep tissue biopsy for identification of pathogens. Material and Methods: It was a prospective observational cross-sectional study. Diabetic foot was defined as per standard guidelines. Careful and meticulous examination of diabetic foot ulcer was done. Two specimens were collected from each wound. The first specimen was a wound swab collected by using Levine technique; another was taken via punch biopsy from the ulcer base. It was a deep tissue sample of 4 mm size. Results: A total of 120 diabetic patients with diabetic foot infection were included in this study. In swab culture 80.83% patients had mono microbial growth, 15% had polymicrobial and 4.10% had no growth. In deep tissue culture 87.50% had mono microbial growth, 2.50% had poly microbial and 10% were sterile. Staphylococcus aureus was most common isolate followed by E. coli. It was observed that though monomicrobial growth was most common in both the types of samples but was higher in deep tissue biopsy than in superficial swab samples. Conclusion: The isolation of microorganism via deep tissue sampling in diabetic foot ulcer patients is more reliable compared to superficial swab samples and a better guide to antibiotic therapy.