Optimization of an Infected Shoe Model for the Evaluation of an Ultraviolet Shoe Sanitizer Device

Onychomycosis and tinea pedis (athlete’s foot) are infections of the nails and skin caused by pathogenic fungi collectively known as dermatophytes. These infections are difficult to treat, and patients often relapse; it is thought that a patient’s footwear becomes infected with these fungal organisms and, thus, is an important reservoir for reinfection. Therefore, it is important to find an effective means for killing the dermatophytes that may have colonized the inner surface of the shoes of patients with superficial fungal infections. In this study, we developed an in vitro model for culturing dermatophytes in footwear and used this model to evaluate the effectiveness of a commercial ultraviolet shoe sanitizer in eradicating the fungal elements residing in shoes. Leather and athletic shoes (24 pairs) were inoculated with either Trichophyton rubrum or Trichophyton mentagrophytes (10⁷ colony-forming units/mL) strains and were placed at 35°C for 4 to 5 days. Next, we compared the ability of swabbing versus scraping to collect microorganisms from infected shoes. Following the optimized method, shoes were infected and were irradiated with one to three cycles of radiation. The inner surfaces of the shoes were swabbed or scraped, and the specimens were cultured for dermatophyte colony-forming units. Leather and canvas shoes were infected to the same extent. Moreover, scraping with a scalpel was overall more effective than was swabbing with a cotton-tipped applicator in recovering viable fungal elements. Irradiation of shoes with one, two, or three cycles resulted in reduction of fungal colonization to the same extent. The developed infected shoe model is useful for assessing the effectiveness of ultraviolet shoe sanitizers. Also, ultraviolet treatment of shoes with a commercial ultraviolet C sanitizing device was effective in reducing the fungal burden in shoes. These findings have implications regarding breaking foot infection cycles. (J Am Podiatr Med Assoc 102(4): 309–313, 2012)