In this study, this report has three valuable characteristics. First, we described the indigenous isolation of a TBF-resistant T. indotineae strain from a Chinese patient with tinea corporis and t. cruris; second, this strain (designated CAMSTi-001) exhibited double resistance with TBF MIC of > 32 µg/mL and ITZ MIC of 1.0 µg/mL; third, regardless of the refractory and relapse for multiple times, the patient finally clinical cured by oral itraconazole pulse therapy and topical clotrimazole cream for 5 weeks.
Since 2019, the number of T. indotineae cases have been reported in India and increased to the whole world, Currently, 76% of the known sequences have been identified in India, 12.8% in the Middle East, 9.6% in Europe, and 1.1% in other countries [23]. Reported ITS genotypes were downloaded from the NCBI database to build a phylogenic tree. The ITS sequence revealed that our isolate was T. indotineae, with 100% similarity with isolates from Asian and European countries. China as a large country with various geographical terrains, the world's largest population, boarding India to the southwest, imbalance of economic developing world et al. There may exist drug resistance in China for long time at a background similar to India of breeding drug-resistance T.indotinea, which should arouse our attention to this new emerging pathogen. It is remarkable that our patient did not travel anywhere and denied contact with animals. It means that China automated induce the TBF and ITZ resistant T. indotineae. Given the large population of China, this problem may be just the tip of the iceberg and potential emergence may be expected. The outbreak of T. indotineae in India is probably mainly due to the unreasonable use of combination creams containing high-potency steroids together with antimycotic and antibiotic agents [24]. In our patient, he once used clobetasol propionate-ketoconazole cream irregularly, which may have promoted resistance. What is worrying is that such abuse is very common in China, as such creams are easily available for any patient to obtain over-the-counter at local pharmacies T. indotineae is more prone than other species of the T. mentagrophytes complex to show resistance to terbinafine resulting in the necessity of rapid identification. Tang et al [21] showed that, other than sequencing, only MALDI-TOF MS can distinguish the species at sufficient (96.97%) confidence from closely related species. In our case, we first used MALDI-TOF MS to identify the isolate and subsequently compared rDNA ITS sequences as taxonomic standard. MALDI-TOF MS is a convenient method and proved sufficient for reliable identification. The T. indotineae specific PCR [25] was positive with our isolate.
In strains retrospectively identified as belonging to the T. mentagrophytes species complex, a significant spread of TBF resistance ranging between 0.2%~ 81% is observed in previous statistics [6]. In accordance with our previous report [6], high MICs (16 µg/mL) of TBF were associated with mutations 1189T > C, 1191C > A, or 1191C > G, which led to amino acid substitutions Phe397Leu or Leu393Phe. Sometimes the mutation was combined with the amino acid substitution Ala448Thr. Strains with moderate to low MICs for TBF (0.125 ~ 0.5 µg/mL) showed the amino acid substitutions Phe415Val, Leu393Ser, His440Tyr or Ala448Thr. These mutations are most often found at Leu393 and Phe397 in SQLE. The isolate in the present study revealed a single mutation of the SQLE gene (Phe397Leu, mutation 1191C > A). While the resistance of T. indotineae to TBF remains common, it seems to be exceptional with ITC-resistance of T. indotineae. Ebert detected the number of 279 T.indotineae strains and found that the MIC of ITC was reported to be around 0.016 mg/mL in 90% of the tested strains, while 10% of the strains showed reduced susceptibility to ITC, with a MIC of 0.5 mg/L. It was emphasized that isolates resistant to both ITC and VRC were more prevalent in TRB-sensitive isolates (42%) than in TRB-resistant isolates (18%) [4]. Thus, it was not very common that the terbinafine-resistant isolate also exhibited high MICs for itraconazole, miconazole, ketoconazole and fluconazole in our case. Several mechanisms of azole resistance in human-pathogenic fungi leading to resistance have been described, including point mutations in genes encoding drug targets, overexpression of those targets, and overexpression of multidrug transporters of the ABC family or major facilitator superfamily transporters (MFS) genes involved in drug efflux [22]. Sequencing the CYP51A and CYP51B genes revealed that no mutations of this gene encoding sterol 14α-demethylase and involving in resistance, which is not consistent with the four different types of Erg11B mutants detected by Anke Burmester [18]. However, overexpression of CYP51A and CYP51B in azole-resistant T. indotineae was also identified, in accordance with the report by Yamada et al [26].
First line systemic treatment for T. indotineae with terbinafine is not recommended due to the high number of SQLE mutant strains. Fluconazole is also to be avoided in the systemic treatment due to the high intrinsic MIC values of T. indotineae strains. In terbinafine-resistant cases, itraconazole as a systemic alternative has been recommended in several studies. However, a significant proportion of T. indotineae strains also shows resistance against itraconazole. Thus, treatment for T. indotineae will be a challenge in the future due to its dual resistance. Use of relatively new agents, such as voriconazole and luliconazole, as well as combination therapy, could be beneficial for recalcitrant T. indotineae infections [27]. In our case, we take itraconazole pulse therapy (0.2 g p.o. BID) and topical clotrimazole cream (twice a day) for 5 weeks with no recurrence of skin lesions until now. It will provide a new measure for the clinician in treating refractory and relapsing dermatophytes.
In summary, the terbinafine- and itraconazole-resistant Trichophyton indotineae has been reported in China, which may be rapidly dissemination after stopping lockdown policy of COVID-19 in the future, with increased the risk of human-to human transmission. The longtime of itraconazole pulse therapy (0.2 g p.o. BID) and topical clotrimazole cream (twice a day) as an option for treating refractory and relapsing dermatophytes.