Diversity of phenotypically non-dermatophyte, non-Aspergillus filamentous fungi causing nail infections: importance of accurate identification and antifungal susceptibility testing

Onychomycosis is most commonly caused by dermatophytes. In this study, we examined the spectrum of phenotypically non-dermatophyte and non-Aspergillus fungal isolates recovered over a 10-year period from nails of patients with onychomycosis in Hong Kong. A total of 24 non-duplicated isolates recovered from 24 patients were included. The median age of the patients was 51 years, and two-thirds of them were males. One-third and two-thirds had finger and toe nail infections respectively. Among these 24 nail isolates, 17 were confidently identified as 13 different known fungal species, using a polyphasic approach. These 13 species belonged to 11 genera and ≥9 families. For the remaining seven isolates, multilocus sequencing did not reveal their definite species identities. These seven potentially novel species belonged to four different known and three potentially novel genera of seven families. 33.3%, 41.7% and 95.8% of the 24 fungal isolates possessed minimum inhibitory concentrations of >1 µg/mL to terbinafine, itraconazole and fluconazole, respectively, the first line treatment of onychomycosis. A high diversity of moulds was associated with onychomycosis. A significant proportion of the isolates were potentially novel fungal species. To guide proper treatment, molecular identification and antifungal susceptibility testing should be performed for these uncommonly isolated fungal species.

甲真菌病（Onychomycosis）最常见的致病原为皮肤癣菌（dermatophytes）。本研究对香港地区10年间从甲真菌病患者指甲样本中分离获得的表型非皮肤癣菌且非曲霉属（Aspergillus）的真菌分离株谱进行了分析。本研究共纳入24株源自24名患者的非重复分离菌株。患者的中位年龄为51岁，其中三分之二为男性；三分之一的感染累及手指甲，三分之二累及脚趾甲。在这24株指甲分离菌株中，研究人员采用多相分类法（polyphasic approach）准确鉴定出其中17株，其分属于13个已知真菌物种，这13个物种隶属于11个属及至少9个科。剩余7株分离菌株经多位点测序（multilocus sequencing）未能明确其确切物种分类地位，这7株潜在新种分别隶属于7个科中的4个已知属与3个潜在新属。24株真菌分离株中，分别有33.3%、41.7%及95.8%的菌株对作为甲真菌病一线治疗药物的特比萘芬（terbinafine）、伊曲康唑（itraconazole）及氟康唑（fluconazole）的最低抑菌浓度大于1 μg/mL。本研究结果表明，与甲真菌病相关的霉菌类群具有高度多样性，且相当比例的分离菌株为潜在新真菌物种。为指导临床合理用药，应对这类罕见分离真菌菌株开展分子鉴定及抗真菌药敏试验。