# Emerging Trimethoprim-Sulfamethoxazole Resistance Among Pathogens Isolated From Diabetic Foot Ulcers: A Case Emphasizing Early Culture-Guided Therapy

## TL;DR

This case study shows how delayed treatment and antibiotic resistance in a diabetic foot ulcer led to complications, emphasizing the need for early culture-guided therapy.

## Contribution

The case highlights emerging trimethoprim-sulfamethoxazole resistance in Staphylococcus aureus from diabetic foot ulcers and advocates for culture-guided treatment.

## Key findings

- Trimethoprim-sulfamethoxazole resistance was observed in Staphylococcus aureus isolated from a diabetic foot ulcer.
- Switching to metronidazole and ciprofloxacin, along with lifestyle and glycemic control, led to full-thickness healing.
- Early culture-guided therapy is critical to managing antibiotic resistance in polymicrobial diabetic ulcers.

## Abstract

Lower extremity ulcers are a major complication of diabetic disease, often leading to a source of infection for patients. Due to delayed wound healing, ulcers quickly develop into extensive lesions leading to infections that are polymicrobial in nature and highly likely to acquire antibiotic resistance. We present the case of a 44-year-old man with poorly controlled type 2 diabetes mellitus who developed an ulcer on the left lower extremity after an episode of mild pruritus. Failure of early patient presentation to the office resulted in the propagation of infection, including areas of depth and necrosis. The ulcer was initially treated with trimethoprim-sulfamethoxazole (SXT) until cultures revealed a polymicrobial infection of Bacteroides fragilis, group B Streptococcus, and Staphylococcus aureus, with resistance to SXT observed exclusively in S. aureus. Furthermore, the ulcer continued to show signs of infection. As a result, medications were adjusted to metronidazole and ciprofloxacin, combined with meticulous wound care, lifestyle modifications, and optimization of glycemic and lipid control. After treatment modifications, the ulcer showed full-thickness healing. This case highlights the evolving challenge of antimicrobial resistance in skin and soft tissue infections. While SXT is commonly used for infected diabetic ulcers, the increasing prevalence of resistant S. aureus strains emphasizes the importance of culture-guided therapy, careful empiric antibiotic selection, and close patient follow-up. With this holistic, patient-centered approach in managing diabetic ulcers, physicians can catch antibiotic resistance early, preventing serious adverse outcomes and improving quality of life.