Comparison of Human and Soil Candida tropicalis Isolates with Reduced Susceptibility to Fluconazole

Abstract

Infections caused by treatment-resistant non-albicans Candida species, such as C. tropicalis, has increased, which is an emerging challenge in the management of fungal infections. Genetically related diploid sequence type (DST) strains of C. tropicalis exhibiting reduced susceptibility to fluconazole circulated widely in Taiwan. To identify the potential source of these wildly distributed DST strains, we investigated the possibility of the presence in soil of such C. tropicalis strains by pulsed field gel electrophoresis (PFGE) and DST typing methods. A total of 56 C. tropicalis isolates were recovered from 26 out of 477 soil samples. Among the 18 isolates with reduced susceptibility to fluconazole, 9 belonged to DST149 and 3 belonged to DST140. Both DSTs have been recovered from our previous studies on clinical isolates from the Taiwan Surveillance of Antimicrobial Resistance of Yeasts (TSARY) program. Furthermore, these isolates were more resistant to agricultural azoles. We have found genetically related C. tropicalis exhibiting reduced susceptibility to fluconazole from the human hosts and environmental samples. Therefore, to prevent patients from acquiring C. tropicalis with reduced susceptibility to azoles, prudent use of azoles in both clinical and agricultural settings is advocated.

Potentially pathogenic yeasts from soil of children’s recreational areas in the city of Łódź (Poland)

“…The rates of isolation of C. krusei, C. guilliermondii, C. lusitaniae, C. kefyr, and C. famata did not vary significantly, whereas those of fluconazole-resistant species C. rugosa, C. inconspicua, and C. norvegensis increased 5-to 10-fold over the 10.5-year study period [20]. It is worth noting that C. tropicalis isolates from Taiwan hospitals and soil samples, revealed strains with reduced susceptibility to azole drugs, which can be of great clinical importance [21]. The isolates recovered from humans and soil, originating from different geographic regions of Taiwan, share the same genome pattern (diploid sequence type).…”

Stepwise Development of a Homozygous S80P Substitution in Fks1p, Conferring Echinocandin Resistance in Candida tropicalis

“…Unfortunately, acquired fluconazole resistance is increasing, with ranges from approximately 7% in Denmark (9) to 9% in a global study (11) and 40% in Japan (12). Based on such findings, echinocandins are increasingly being utilized in the management of candidiasis caused by C. tropicalis (10,(13)(14)(15).…”

Calcineurin Controls Hyphal Growth, Virulence, and Drug Tolerance of Candida tropicalis

“…Thus, calcineurin is, in general, required for the virulence of C. tropicalis and C. dubliniensis in both murine systemic and ocular infection models, while Crz1 is required for the virulence of C. tropicalis and C. dubliniensis only in a murine systemic infection model and not in an ocular infection model, suggesting a specific niche requirement (bloodstream versus ocular surface) of Crz1 in both C. tropicalis and C. dubliniensis (27). In addition to being frequently isolated from patients (11,17,(60)(61)(62), C. tropicalis has also been isolated from the mouse intestine (where it constitutes up to 65% of the overall fungal component) (63) and environmental compost and soil (11,64). Previous studies suggest that C. tropicalis can be transferred by hand-tohand contact (65), indicating a potential route for human-human transmission.…”

“…Within the last few years, C. tropicalis drug-tolerant or -resistant isolates have frequently been isolated from patients and environmental samples (10)(11)(12)(13)(14). For example, Garcia-Effron et al showed that 7.5% (3/40) of clinical C. tropicalis isolates were caspofungin resistant owing to amino acid substitutions in beta-1,3-glucan synthase (Fks1p) that resulted in caspofungin-based therapy failures (10).…”

“…An Asian national antifungal surveillance program found reduced susceptibility of C. tropicalis to fluconazole (12). Recently, Yang et al reported that C. tropicalis strains isolated from environmental soil also showed reduced susceptibility to medical and agricultural azoles, advocating for the prudent use of azoles in agriculture (11). So far, few studies have focused on C. tropicalis drug resistance mechanisms.…”