Molecular identification of Trichophyton benhamiae in Strasbourg, France: a 9-year retrospective study

Trichophyton benhamiae is a zoophilic dermatophyte transmitted to humans mostly from guinea pigs and occasionally other animals. It presents two distinct phenotypes: yellow and white. T. benhamiae was formerly known as Trichophyton species of Arthroderma benhamiae; it was considered part of the T. mentagrophytes species complex, and some authors have incorrectly described the yellow phenotype of T. benhamiae as T. mentagrophytes var. porcellae. Identification of T. benhamiae has been difficult, as it was described under more than three names, two phenotypes, and in several different possible host species. During the past 15 years, human infections due to this dermatophyte have been increasingly reported all over the world. In order to better understand the local epidemiology of T. benhamiae and to compare it to other European countries, we performed a 9-year retrospective study in the Strasbourg University Hospital. We studied 41 dermatophytes (38 isolated from humans and 3 from guinea pigs) identified as T. mentagrophytes var. porcellae or A. benhamiae from January 2008 to December 2016 and verified their identification by ITS (Internal Transcribed Spacer) sequencing. ITS sequencing was performed in 35 of the 41 strains, and they were identified as T. benhamiae (33), T. bullosum (1), and T. eriotrephon (1). The other six remaining strains were identified according to morphology as T. mentagrophytes var. porcellae, name incorrectly used since 2010 for the yellow phenotype of T. benhamiae. ITS sequencing is recommended for accurate identification of this dermatophyte and the culture phenotype (yellow or white) should be specified.