Microbial isolates and their antimicrobial susceptibilities in inframalleolar foot infections

Background: Foot infections are especially common among diabetic individuals and often contribute to limb loss. We investigated the microbiology of foot infections in our hospital to further understand the microbes involved and to assist in identifying potential empiric oral antibiotic regimens for foot infections.

Methods: All moderate/severe inframalleolar foot infections that were drained surgically at a single center during a single calendar year were included. Initial isolates obtained intra-operatively were reviewed.

Results: A total of 39 patients underwent operative drainage, of whom 34 (87%) had diabetes mellitus. Fifty-two total specimens were obtained, consisting of 26 fluid swabs, 12 soft-tissue specimens, and 11 bone specimens. Nineteen (49%) of the specimens were obtained from toe wounds, 16 (41%) from forefoot wounds, two (5%) from midfoot wounds, and two (5%) from heel wounds. Most specimens (71%) were polymicrobial, yielding a mean of 2.2 isolates. In all, 100 individual isolates, encompassing 39 different bacterial organisms, were identified (55 gram-positive aerobes, 33 gram-negative aerobes, 11 anaerobes, and one fungus). Enterococcus species and Staphylococcus aureus were the most common bacteria, each representing 13% of isolates. Only 9% of isolates were methicillin-resistant S. aureus. Obtaining multiple specimens (e.g., both fluid and tissue) increased the yield for identification of organisms. Oral antibiotics provided adequate coverage for gram-positive organisms but not for gram-negative organisms.

Conclusions: Foot infections are typically polymicrobial and may involve a wide variety of microbes. Initial gram-stain results could be used to choose better initial empiric antimicrobial therapy for such infections.