Discontinuation of echinocandin and azole treatments led to the disappearance of an FKS alteration but not azole resistance during clonal Candida glabrata persistent candidaemia

Candida glabrata is the second leading cause of candidemia in U.S. hospitals. Current guidelines suggest that an echinocandin be used as the primary therapy for the treatment of C. glabrata disease due to the high rate of resistance to fluconazole. Recent case reports indicate that C. glabrata resistance to echinocandins may be increasing. We performed susceptibility testing on 1,380 isolates of C. glabrata collected between 2008 and 2013 from four U.S. cities, Atlanta, Baltimore, Knoxville, and Portland. Our analysis showed that 3.1%, 3.3%, and 3.6% of the isolates were resistant to anidulafungin, caspofungin, and micafungin, respectively. We screened 1,032 of these isolates, including all 77 that had either a resistant or intermediate MIC value with respect to at least one echinocandin, for mutations in the hot spot regions of FKS1 and FKS2, the major mechanism of echinocandin resistance. Fifty-one isolates were identified with hot spot mutations, 16 in FKS1 and 35 in FKS2. All of the isolates with an FKS mutation except one were resistant to at least one echinocandin by susceptibility testing. Of the isolates resistant to at least one echinocandin, 36% were also resistant to fluconazole. Echinocandin resistance among U.S. C. glabrata isolates is a concern, especially in light of the fact that one-third of those isolates may be multidrug resistant. Further monitoring of U.S. C. glabrata isolates for echinocandin resistance is warranted.

The echinocandin antifungal drugs inhibit synthesis of the major fungal cell wall polysaccharide β(1,3)-glucan. Echinocandins have good efficacy against Candida albicans but reduced activity against other Candida species, in particular Candida parapsilosis and Candida guilliermondii. Treatment of Candida albicans with a sub-MIC level of caspofungin has been reported to cause a compensatory increase in chitin content and to select for sporadic echinocandin-resistant FKS1 point mutants that also have elevated cell wall chitin. Here we show that elevated chitin in response to caspofungin is a common response in various Candida species. Activation of chitin synthesis was observed in isolates of C. albicans, Candida tropicalis, C. parapsilosis, and C. guilliermondii and in some isolates of Candida krusei in response to caspofungin treatment. However, Candida glabrata isolates demonstrated no exposure-induced change in chitin content. Furthermore, isolates of C. albicans, C. krusei, C. parapsilosis, and C. guilliermondii which were stimulated to have higher chitin levels via activation of the calcineurin and protein kinase C (PKC) signaling pathways had reduced susceptibility to caspofungin. Isolates containing point mutations in the FKS1 gene generally had higher chitin levels and did not demonstrate a further compensatory increase in chitin content in response to caspofungin treatment. These results highlight the potential of increased chitin synthesis as a potential mechanism of tolerance to caspofungin for the major pathogenic Candida species.

Minimum inhibitory concentration (MIC) data from the SENTRY Antimicrobial Surveillance Program generated by reference methods were analysed to compare the antifungal resistance profiles and species distribution of Candida bloodstream infection (BSI) isolates obtained from patients in the Intensive Care Unit (ICU) and those from non-ICU locations. Results from 79 medical centres between 2008 and 2009 were tabulated. MIC values were obtained for anidulafungin, caspofungin, micafungin, fluconazole, posaconazole and voriconazole. Recently revised Clinical and Laboratory Standards Institute breakpoints for resistance were employed. A total of 1752 isolates of Candida spp. were obtained from ICU (779; 44.5%) and non-ICU (973; 55.5%) settings. The frequency of ICU-associated Candida BSI was higher in Latin America (56.5%) compared with Europe (44.4%) and North America (39.6%). The frequency of candidaemia in the ICU decreased both in Latin America and North America over the 2-year study period. Approximately 96% of isolates both in ICU and non-ICU settings were caused by only five species (Candida albicans, Candida glabrata, Candida parapsilosis, Candida tropicalis and Candida krusei). Resistance both to azoles and echinocandins was uncommon in ICU and non-ICU settings. Overall, fluconazole resistance was detected in 5.0% of ICU isolates and 4.4% of non-ICU isolates. Candida glabrata was the only species in which resistance to azoles and echinocandins was noted, and this multidrug-resistant phenotype was found in both settings. In conclusion, the findings from this global survey indicate that invasive candidiasis can no longer be considered to be just an ICU-related infection, and efforts to design preventive and diagnostic strategies must be expanded to include other at-risk populations and hospital environments. Concern regarding C. glabrata must now include resistance to echinocandins as well as azole antifungal agents. Copyright © 2011 Elsevier B.V. and the International Society of Chemotherapy. All rights reserved.