We aim to demonstrate the value of deep tissue biopsies to guide antimicrobial treatment of diabetic ulcers. Some recent studies have advocated the role of superficial swabs to guide antibiotic treatment in comparison to deep tissue biopsies previously perceived as the gold standard of microbiology diagnosis. We performed a retrospective analysis of microbiology culture results of patients with infected diabetic ulcers comparing superficial versus deep biopsy microbiology results.

Forty-one diabetic ulcers in 41 patients were included. The mean numbers of isolates from soft tissue and bone biopsies were 2.1 and 1.8 respectively. 39/41 combined soft tissue and bone biopsies were culture positive. The most prevalent organism seen in deep samples was Staphylococcus aureus (14) followed by anaerobes (9), and enterococcus (9). In superficial swab cultures 21 patients (51%) cultured non-specific, mixed skin flora and enteric species. The remaining 20 patients cultured Staphylococcus aureus (11), Streptococcus (6), Pseudomonas (2) and anaerobes (6).

Three superficial swabs matched deep tissue biopsy cultures. 16 deep biopsies grew organisms seen none specifically in superficial swab cultures with 22 deep tissue biopsies cultures growing organisms not seen on superficial swab with 8 being anaerobes.

We have shown that in 54% of cases, deep tissue cultures isolated organisms that were not grown by superficial swab cultures. We highlight the importance of deep tissue biopsies to guide effective treatment.