The association of Yarrowia lipolytica with onychomycosis

Onychomycosis, a common fungal nail infection, is typically caused by dermatophytes or <i>Candida</i> species, but rare fungal pathogens can also be involved. We describe a 20-year-old woman with persistent nail shedding who was unresponsive to standard antifungal treatments. Microscopic nail examination, fungal culture, and ITS sequencing repeatedly identified the presence of <i>Yarrowia lipolytica</i> (formerly <i>Candida lipolytica</i>), a dimorphic yeast more often associated with systemic bloodstream infections and not previously identified in patients with onychomycosis. Susceptibility testing revealed the resistance of <i>Y. lipolytica</i> isolates to multiple antifungal azoles, complicating future treatment strategies for the patient. Commonly found in hydrocarbon-rich environments and an important organism for biotechnology, <i>Y. lipolytica</i> has industrial applications but is also capable of causing opportunistic infections in vulnerable patient populations. This case highlights the importance of thorough microbial identification and susceptibility testing in cases of treatment-resistant onychomycosis.