An 18-year-old white male high-school student visits the family physician complaining of a diffuse, painful rash extending from his midthigh to his navel region. In recounting the history of the rash, he indicates that one of his football teammates gave him topical hydrocortisone to treat a minor groin rash. A KOH scraping of the lesion reveals hyaline hyphae and a portion of the scraping is submitted for culture. A schematic of the microscopic observation of the culture is shown below. The most likely etiology is