Antifungal Resistance among Less Prevalent Candida Non-albicans and Other Yeasts versus Established and under Development Agents: A Literature Review

Fungal diseases and antifungal resistance continue to increase, including those caused by rare or emerging species. However, the majority of the published in vitro susceptibility data are for the most common fungal species. We reviewed the literature in order to pool reference minimal inhibitory concentration (MIC) data (Clinical and Laboratory Standards Institute—CLSI and European Committee on Antimicrobial Susceptibility—EUCAST) for rare/non-prevalent Candida and other yeast species. MIC results were compared with those for Candida albicans, C. glabrata, and C. krusei. Data were listed for twenty rare and emerging Candida spp., including C. auris, as well as two Cryptococcus spp., two Trichosporon spp., Saccharomyces cerevisiae and five Malassezia spp. The best detectors of antimicrobial resistance are the breakpoints, which are not available for the less common Candida species. However, epidemiological cutoff values (ECVs/ECOFFs) have been calculated using merely in vitro data for both reference methods for various non-prevalent yeasts and recently the CLSI has established ECVs for other Candida species. The ECV could identify the non-wild type (NWT or mutants) isolates with known resistance mechanisms. Utilizing these ECVs, we were able to report additional percentages of NWT, especially for non-prevalent species, by analyzing the MIC distributions in the literature. In addition, since several antifungal drugs are under development, we are listing MIC data for some of these agents.