Clonal spread and azole-resistant mechanisms of non-susceptible Candida albicans isolates from vulvovaginal candidiasis patients in three Shanghai maternity hospitals

In our multicenter study, 43 fluconazole non-susceptible and 45 fluconazole-susceptible isolates were collected from vulvovaginal candidiasis (VVC) patients from three Shanghai maternity hospitals to analyze their molecular epidemiological features and fluconazole resistant mechanisms. Cross-resistance to fluconazole, itraconazole and voriconazole was observed in 53.5% of the nonsusceptible isolates. Though we acquired 12 clonal complexes (CCs) of diploid sequence types (DSTs) in clinical isolates by a multilocus sequence typing method, fluconazole nonsusceptible isolates all belonged to CC69 with a predominant genotype of DST 79. Increased expressions of efflux pump genes (CDR1, CDR2, and MDR1) were observed only in minor fluconazole non-susceptible isolates by real-time quantitative polymerase chain reaction (PCR). However, ERG11 genes of fluconazole SDD and resistant isolates had significantly higher expression levels than fluconazole-susceptible isolates. Moreover, 13 distinct amino acid substitutions in Erg11p were found in clinical isolates. Three of the substitutions were novel amino acid substitutions (T123I, P98S, and Y286D), which were not in the susceptible isolates. Only two heterozygous amino acid substitutions (A18P/A and R365G/R) in Erg3p were found in two isolates with cross-resistance to fluconazole, itraconazole, and voriconazole. Taken together, we observed the clonal spread of CC69 in fluconazole non-susceptible isolates of Candida albicans from VVC patients with the dominant genotype DST79. ERG11 gene mutations and overexpression predominantly contributed to fluconazole resistance instead of the more common increased expressions of efflux pump genes (CDR1, CDR2, and MDR1).