Prevalence and antifungal susceptibility of Wickerhamomyces anomalus in a tertiary care center

Abstract Poster session 1, September 21, 2022, 12:30 PM - 1:30 PM Objectives The spectrum of yeast species causing fungemia has been expanding with emergence of many unusual pathogenic species. One such species is Wickerhamomyces anomalus which has been recognized as an important cause of nosocomial fungemia in neonates and pediatric patients. We evaluated antifungal susceptibility and the burden of antifungal resistance in W. anomalus. Methods Species identification of the isolates was performed using MALDI-TOF MS. Antifungal susceptibility testing was done according to the CLSI broth microdilution method following the M27- A3 protocol. C. parapsilosis ATCC22019 and C. krusei ATCC6258 were used as quality control strains. The lowest azole or echinocandin concentration inhibiting 50% visible growth and for amphotericin B, 100% growth-inhibition was taken as minimum inhibitory concentration (MIC). As species-specific breakpoints for resistance are not available for W. anomalus, the susceptibility data was interpreted using CLSI breakpoints (M60 1st edition) as surrogate markers of resistance. Results A total of 633 W. anomalous isolated over a 5-year study period from January 2016, through December 2019 at our center, were evaluated for susceptibility to amphotericin B, fluconazole, voriconazole, caspofungin, anidulafungin, and micafungin. The majority of W. anomalus was isolated from neonates (57.1%) followed by other pediatric patients (40.1%). Antifungal therapy was administered in 21% of the patients with fluconazole as the commonest antifungal agent (67.3%) followed by amphotericin B, 31.2%, and voriconazole (1.4%). For amphotericin B, 99.6% (602/604) of the isolates exhibited MIC ≤ 2 mg/l. For fluconazole, 81% of the isolates were susceptible while 19% of the isolates exhibited reduced susceptibility of which 3% were resistant, and 16% exhibited susceptible dose-dependent phenotype. Of all the fluconazole-resistant isolates, two (0.3%) isolates were cross-resistant to voriconazole. Among echinocandins, the resistant rate of 2.8%, 1.2%, and 1.6% wase noted in caspofungin, anidulafungin, and micafungin, respectively. Conclusions Wickerhamomyces anomalus exhibited intrinsic susceptibility to all the antifungal agents evaluated. A substantial resistance to fluconazole was noted in this species while resistance to echinocandins was low.