Superantigens of Staphylococcus aureus from patients with diabetic foot ulcers

Diabetic foot ulcer (DFU) infections are challenging. Staphylococcus aureus is the most commonly isolated pathogen in DFUs. Superantigens (SAgs) are causative in many S. aureus infections. We hypothesized both that DFU S. aureus will produce large SAg numbers, consistent with skin infections, and that certain SAgs will be overrepresented. We assessed the SAg and α-toxin profile of isolates from patients with DFU, compared with profiles of isolates from other sources.

Twenty-five S. aureus isolates from patients with DFU were characterized. Polymerase chain reaction was used to detect genes for methicillin-resistance and SAgs. Some SAgs and the α-toxin were quantified. We compared the SAg profile of DFU isolates with SAg profiles of S. aureus isolates from skin lesions of patients with atopic dermatitis and from vaginal mucosa of healthy individuals.

Most DFU isolates were methicillin susceptible (64%), with USA100 the most common clonal group. The SAg gene profile of DFU isolates most closely resembled that of isolates from patients with atopic dermatitis, with the highest number of different SAg genes per isolate and a high prevalence of staphylococcal enterotoxin D and the enterotoxin gene cluster. DFU isolates also had a high prevalence of staphylococcal enterotoxin-like X.

Comparison of the SAg profile of DFU isolates to SAg profiles of skin lesion isolates and vaginal mucosa isolates revealed that the SAg profile of DFU isolates was more similar to that of skin lesion isolates. SAgs offer selective advantages in facilitating DFU infections and suggest that therapies to neutralize or reduce SAg production by S. aureus may be beneficial in management of patients with DFU.