A 60-year-old woman complains to a physician because several of her toenails are discolored. Physical examination demonstrates crumbling, friable nails with distal-lateral separation from the nail bed. Hyperkeratotic debris is present under the affected pa of the nail. Which of the following is the most likely pathogen?

The patient has a fungal nail infection. These infections are seen most commonly in the elderly, and are usually caused by dermatophyte infection, typically Trichophyton rubrum, Trichophyton mentagrophytes, or Epidermophyton floccosum. Some of the more superficial lesions can be removed by simply scraping the fungus off the nail. Systemic fungal therapy (notably terbinafine) of months duration (because nails are grown so slowly) may be required for deeper nail lesions. Aspergillus may be a lung saprophyte or cause invasive disease. Candida is a rare cause of fungal nail infection. Associate Mucor with sinonasal infection. Ref: Ray C.G., Ryan K.J. (2010). Chapter 44. Dermatophytes, Sporothrix, and Other Superficial and Subcutaneous Fungi. In C.G. Ray, K.J. Ryan (Eds), Sherris Medical Microbiology, 5e.