Trichophyton mentagrophytes

Nomenclature

Along with closely related T. interdigitale, the species has been traditionally treated as a part of polyphyletic assemblage, named "T. mentagrophytes sensu lato". From 1999 to 2017 the two species have been collectively referred to as T. interdigitale, while the name "T. mentagrophytes" has been used for current T. quinckeanum. Trichophyton interdigitale seems to be strictly anthropophilic, and is associated with foot and nail infections.

Mating and meiosis

Trichophyton mentagrophytes is capable of mating. This species is also able to undergo meiosis. The haploid chromosome complement of T. mentagrophytes is four. The fusion of haploid nuclei (karyogamy) preceding meiosis occurs in the penultimate cell of a typical crozier, an anatomical feature of the sexual phase of many fungi in the Division Ascomycota.

Effect in mammals

Trichophyton mentagrophytes is one of three common fungi which cause ringworm in companion animals and frequently isolated from dogs, cats, rabbits, guinea pigs and other rodents.

It is the most common or one of the most common fungi that cause zoonotic skin disease (i.e., transmission of mycotic skin disease from species to species).

While it is considered a zoophilic species, it is also the second-most commonly isolated fungus causing tinea infections in humans, and at least some genetic variants possess the potential of human-to-human transmission, e.g. Type VII and Type VIII.

Since 2002 cases were reported in Nigerian sex workers, in 2021 in men who have sex with men in France and as of 2024 in New York City.

Pathology

Out of all species considered to be a part of the Trichophyton mentagrophytes complex, T. mentagrophytes causes the most severe form of symptoms in humans, including pustules, abscesses and ulceration, and induces a strong inflammatory response in the infected tissue. It causes infections mostly on the trunk, legs and arms (tinea corporis) or on the scalp (tinea capitis), where it mainly targets the keratinocytes of the epidermis.

T. mentagrophytes induces robust cell death in keratinocytes, more so than the other species in the complex. It causes these effects through different components: necrosis mainly through its hyphae, and apoptosis through its supernatant. The apoptotic effect of the supernatant is attributed to SN-38, a compound best known as an active metabolite of irinotecan used as a cancer medicine.

Epidemiology

Particular genetic variants of the fungus have distinct geographic ranges.

For studies on the epidemiology of T. mentagrophytes, two molecular strain typing techniques are available. The first one is based upon amplification of nontranscribed spacer of ribosomal DNA, and the second one involves a comparison of internal transcribed spacer sequences within defined boundaries.

Treatment and drug resistance

In T. mentagrophytes, antifungal drug resistance is mainly associated with Type VIII isolates. Drug-resistant T. mentagrophytes strains have been found in many places across Asia and Europe. India is the most affected country, with the rate of microbiological resistance to terbinafine estimated at 11.4%. There are also reports on terbinafine-resistant Type II isolates from Japan and Denmark.

References

References

1. Nenoff, Pietro. (April 2019). "The current Indian epidemic of superficial dermatophytosis due to Trichophyton mentagrophytes —A molecular study". Mycoses.
2. (June 2025). "Zoonotic and Anthropophilic Trichophyton mentagrophytes Complex Infection in Human: An Update and Narrative Review". Mycoses.
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4. (1968). "Meiosis in Arthroderma benhamiae (=Trichophyton mentagrophytes)". Sabouraudia.
5. Zucker, Jason. (2024). "Notes from the Field: Trichophyton mentagrophytes Genotype VII — New York City, April–July 2024". MMWR. Morbidity and Mortality Weekly Report.
6. Ma, Yubo. (2023-03-01). "Dual RNA-Sequencing and Liquid Chromatography–Mass Spectrometry Unveil Specific Insights on the Pathogenicity of Trichophyton mentagrophytes Complex". Journal of Investigative Dermatology.
7. Pharmacia & Upjohn Company LLC. (June 2024). "CAMPTOSAR".
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10. (2010). "Signature polymorphisms in the internal transcribed spacer region relevant for the differentiation of zoophilic and anthropophilic strains of ''Trichophyton interdigitale'' and other species of ''T. mentagrophytes sensu lato''". British Journal of Dermatology.
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15. (2012). "Molecular identification and phylogenesis of dermatophytes isolated from rabbit farms and rabbit farm workers". Veterinary Microbiology.
16. (2016). "Epizootic and epidemic dermatophytose outbreaks caused by ''Trichophyton mentagrophytes'' from rabbits in Portugal, 2015". Mycoses.
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21. (2020). "MIC and upper limit of wild-type distribution for 13 antifungal agents against a ''Trichophyton mentagrophytes-Trichophyton interdigitale'' complex of Indian origin". Antimicrobial Agents and Chemotherapy.