ABSTRACT
Objective:To compare the in vitro susceptibility of fluconazole-resistant Candida albicans strains from superficial and deep infections to 8 antifungal drugs, and to compare drug resistance mutations in these strains. Methods:According to the Clinical and Laboratory Standards Institute (CLSI) protocol M27-A4, 26 deep infection-derived and 33 superficial infection-derived drug-resistant Candida albicans strains were tested for in vitro susceptibility to 8 antifungal drugs (fluconazole, voriconazole, itraconazole, posaconazole, amphotericin B, fluorocytosine, terbinafine, and micafungin) alone or in combination. DNA was extracted from all drug-resistant strains, and mutations in 3 drug resistance genes, including ERG3, ERG11 and FUR1, were detected by PCR. Normally distributed measurement data with homogeneous variance were compared between two groups by using two-independent-sample t test, non-normally distributed measurement data with non-homogeneous variance were compared using Mann-Whitney U test, and enumeration data were compared using chi-square test. Results:The minimum inhibitory concentrations (MICs) of fluconazole, itraconazole, voriconazole, posaconazole and fluorocytosine all significantly differed between the superficial infection group and deep infection group (all P < 0.05) , while there was no significant difference in the MIC of amphotericin B or micafungin between the two groups (both P > 0.05) . The MIC of terbinafine was >64 μg/ml in 96.6% of the above strains, so could not be compared between groups. As combination drug susceptibility testing revealed, the combination of terbinafine with azoles (fluconazole, voriconazole, itraconazole or posaconazole) showed synergistic inhibitory effects against 15 Candida albicans strains (7 strains from deep infections, 8 strains from superficial infections) , with fractional inhibitory concentration (FIC) indices being 0.033 to 0.187; no marked synergistic effect was observed in the combinations between fluorocytosine and azoles, between fluorocytosine and amphotericin B, or between amphotericin B and fluconazole, with the FIC indices being 0.56 to 1.125. The missense mutation V351A in the ERG3 gene was identified in all the 33 (100%) superficial infection-derived strains, as well as in 13 (50%) deep infection-derived strains, and the mutation A353T in the ERG3 gene was identified in 4 (15%) deep infection-derived strains; as for the ERG11 gene, missense mutations identified in the superficial infection-derived strains included I437V (32 strains, 97%) , Y132H (23 strains, 70%) , T123I (16 strains, 48%) , K128T (6 strains, 18%) , D116E (5 strains, 15%) , A114S (4 strains, 12%) , E266D (2 strains, 6%) , G448E (2 strains, 6%) , and G465S (2 strains, 6%) , while missense mutations identified in the deep infection-derived strains included I437V (23 strains, 88%) , E266D (13 strains, 50%) , E260G (5 strains, 19%) , and V488I (4 strains, 15%) ; the missense mutation R101C in the FUR1 gene was identified in 11 (33%) superficial infection-derived strains, but not identified in deep infection-derived strains. Conclusion:The drug susceptibility and drug resistance mutations differed to some extent between superficial infection- and deep infection-derived fluconazole-resistant Candida albicans strains.