Correlation between Azole Susceptibilities,Genotypes, and ERG11 Mutations in Candida albicans Isolates Associated with Vulvovaginal Candidiasis in China

The relationship between susceptibilities to fluconazole and itraconazole and microsatellite CAI genotypes were examined from a total of 154 Candida albicans isolates (97 isolates causing vulvovaginitis in Chinese women and 6 vaginal isolates and 51 oral cavity isolates from asymptomatic carriers). The two dominant genotypes, CAI 30-45 (45 isolates) and CAI 32-46 (33 isolates), associated with vulvovaginitis showed significantly different azole susceptibility patterns with strong statistical support. CAI 32-46 isolates were usually less susceptible to both fluconazole and itraconazole than CAI 30-45 isolates and than the oral isolates with other diversified CAI genotypes. Remarkably different mutation patterns in the azole target gene ERG11 were correspondingly observed among C. albicans isolates representing different genotypes and sources. Isolates with the same or similar CAI genotypes usually possessed identical or phylogenetically closely related ERG11 sequences. Loss of heterozygosity in ERG11 was observed in all the CAI 32-46 isolates but not in the CAI 30-45 isolates and most of the oral isolates sequenced. Compared with the ERG11 sequence of strain SC5314 ({"type":"entrez-nucleotide","attrs":{"text":"X13296","term_id":"2503","term_text":"X13296"}}X13296), two homozygous missense mutations (G487T and T916C) leading to two amino acid changes (A114S and Y257H) in Erg11p were found in CAI 32-46 isolates. The correlation between azole susceptibility and C. albicans genotype may be of potential therapeutic significance.Vulvovaginal candidiasis (VVC) is a common vaginal infection, affecting up to 75% of women of child-bearing age at least once in their lifetime (7, 21, 22). The most frequent cause of VVC is Candida albicans, which is responsible for 70 to 90% of vulvovaginitis cases. Non-C. albicans species of Candida, predominantly Candida glabrata, are responsible for the remainder of cases (21). On the basis of the severity of symptoms, frequency, and causative agents, VVC is usually classified as either uncomplicated (mild and sporadic) or complicated (recurrent, severe, or caused by non-C. albicans species) (7, 21). Ten to 20% of women suffer complicated VVC in their lifetime (21). When properly diagnosed, uncomplicated VVC may be treated easily and reliably. However, complicated VVC often causes long-term physical and mental discomfort, significant economic burden from treatments, and considerable negative effect on sexual relations (21-23).At present, prolonged suppressive therapy using fluconazole is recommended as the standard management for chronic, recurrent Candida vulvovaginitis (23). Therefore, there is a great concern about the emergence and spread of azole resistance of C. albicans isolates associated with VVC. Indeed, susceptibility testing of VVC-causing isolates has been performed in different countries and regions of the world (1, 2, 4, 5, 6, 13-15, 17, 18, 20, 24). Although relatively high frequencies of fluconazole- and/or itraconazole-resistant C. albicans isolates causing VVC have been observed in a few reports (13, 20, 24), most studies failed to identify any clear correlation between azole susceptibility and VVC association among C. albicans isolates (1, 2, 4, 5, 6, 14, 15, 17, 18).Recently, we compared the genotype distribution patterns among independent C. albicans isolates associated with VVC in Chinese women and those from various extragenital sites by using the polymorphic microsatellite locus CAI (8, 11). The results showed that the CAI genotypes of C. albicans isolates from extragenital sites were highly diversified. In contrast, isolates associated with VVC from unrelated patients were more homogeneous and belonged to only a few genotypes, with two genotypes, CAI 30-45 and CAI 32-46, being the most common. These two dominant genotypes were rarely found among isolates from extragenital sites (11). In addition, the distribution of the dominant genotypes correlated positively with the severity of VVC (8, 11). These results suggested that C. albicans isolates with genotypes CAI 30-45 and CAI 32-46 might be more virulent and/or more resistant to the commonly used azole drugs than those with other genotypes as causative agents of vaginal infection.Antifungal susceptibility testing using the Etest method revealed that the C. albicans isolates causing VVC in Chinese women were generally susceptible to fluconazole, amphotericin B, ketoconazole, and flucytosine; however, 19.1% of the isolates could be interpreted as being resistant to itraconazole in vitro. Interestingly, most of the itraconazole-resistant isolates belonged to a specific genotype (13). Contrary to the report described above, recent susceptibility testing and microsatellite typing of vulvovaginitis-causing Candida isolates from Europe did not find an association between azole resistance and any particular genotype cluster among C. albicans isolates (1). In the present study, fluconazole and itraconazole susceptibilities of the C. albicans isolates with the dominant genotypes CAI 30-45 and CAI 32-46 from VVC patients were compared with those of isolates possessing other minor genotypes and of isolates from the oral cavity by using the standard broth microdilution method. Furthermore, ERG11 (encoding lanosterol-14-α-demethylase, the target of azoles) gene sequences of C. albicans isolates representing different genotypes and sources were determined. The correlation between azole susceptibilities, genotypes, and ERG11 mutations was examined.