Molecular Epidemiology and Antifungal Susceptibility of Trichophyton Isolates in Greece: Emergence of Terbinafine-Resistant Trichophytonmentagrophytes Type VIII Locally and Globally

Abstract

Trichophyton isolates with reduced susceptibility to antifungals are now increasingly reported worldwide. We therefore studied the molecular epidemiology and the in vitro antifungal susceptibility patterns of Greek Trichophyton isolates over the last 10 years with the newly released EUCAST reference method for dermatophytes. Literature was reviewed to assess the global burden of antifungal resistance in Trichophyton spp. The in vitro susceptibility of 112 Trichophyton spp. molecularly identified clinical isolates (70 T. rubrum, 24 T. mentagrophytes, 12 T. interdigitale and 6 T. tonsurans) was tested against terbinafine, itraconazole, voriconazole and amorolfine (EUCAST E.DEF 11.0). Isolates were genotyped based on the internal transcribed spacer (ITS) sequences and the target gene squalene epoxidase (SQLE) was sequenced for isolates with reduced susceptibility to terbinafine. All T. rubrum, T. interdigitale and T. tonsurans isolates were classified as wild-type (WT) to all antifungals, whereas 9/24 (37.5%) T. mentagrophytes strains displayed elevated terbinafine MICs (0.25–8 mg/L) but not to azoles and amorolfine. All T. interdigitale isolates belonged to ITS Type II, while T. mentagrophytes isolates belonged to ITS Type III* (n = 11), VIII (n = 9) and VII (n = 4). All non-WT T. mentagrophytes isolates belonged to Indian Genotype VIII and harbored Leu393Ser (n = 5) and Phe397Leu (n = 4) SQLE mutations. Terbinafine resistance rates ranged globally from 0–44% for T. rubrum and 0–76% for T. interdigitale/T. mentagrophytes with strong endemicity. High incidence (37.5%) of terbinafine non-WT T. mentagrophytes isolates (all belonging to ITS Type VIII) without cross-resistance to other antifungals was found for the first time in Greece. This finding must alarm for susceptibility testing of dermatophytes at a local scale particularly in non-responding dermatophytoses.

Increasing Terbinafine Resistance in Danish Trichophyton Isolates 2019–2020

“…SQLE profiling showed that the majority of terbinafine resistance in Danish isolates was caused by F397L, leading to high terbinafine MICs (0.5->4 mg/L). This was followed by L393F and L393S, which are also acknowledged causes of resistance in various countries, mainly in Asia and Europe [19]. One T. rubrum isolate with an L437P substitution had a terbinafine MIC of 1 mg/L, suggesting that this novel alteration may be of clinical relevance although this remains to be confirmed.…”

“…mentagrophytes SC, an actual increase in resistance seems most likely. Since the first detection in 2018, we have found an additional six patients with terbinafine-resistant T. indotineae, which has spread rapidly in India and surrounding regions and also been found in an increasing number of European countries [19][20][21]23,42]. This is worrisome, as T. indotineae may establish itself in the Danish environment and cause a local epidemic.…”

“…The cause of this outbreak has been speculated to be driven by the uncontrolled over-the-counter sale of topical cream containing both steroids, antifungals and antibiotics [14]. T. indotineae has subsequently been reported from several other countries including Japan, Cambodia, Iran, Bahrain, Switzerland, Greece, Finland, and Germany and is thought introduced by inhabitants or visitors from the Indian subcontinent [2,[15][16][17][18][19][20][21]. As dermatophytes are slow growing, PCR is increasingly applied for diagnostics, but current methods are unable to differentiate between T. mentagrophytes/T.…”

Antifungal Resistance in Dermatophytes: Genetic Considerations, Clinical Presentations and Alternative Therapies

“…ITS sequencing defined these nine isolates as T. mentagrophytes type VIII, five of them bearing the F397L substitution, and the L393F substitution for the other four strains. No elevated MICs were reported for azoles or amorolfine in the study [29]. These reports from Europe show that terbinafine resistance is not only a problem for India, and even if the situation is not yet alarming, resistant strains are circulating in European countries and can rapidly spread and become a major public health concern.…”

Terbinafine Resistance in Dermatophytes: A French Multicenter Prospective Study

“…Although T. indotineae accounts for the majority of cases, cases of TerR T. rubrum have also been reported in the Indian outbreak [ 19 ]. Afterwards, population flows, associated with increased travel and migration, have allowed the spread of TerR isolates to different European countries [ 20 , 21 , 22 ] altering the local epidemiology of dermatophytes [ 23 ]. We and others have recently reported a series of TerR dermatophytoses due to T. indotineae in France [ 24 , 25 ] but the current relative frequency of TerR and of T. indotineae isolates remains unknown.…”