Phenotypic and Genotypic Characterization of Intestinal Candida spp. in Tunisia

Background: Yeasts naturally colonize the mammalian digestive tract and play an important role in health and disease. This community is composed of commensal yeasts, mostly Candida and Saccharomyces described as a part of the intestinal mycobiome and could be associated with resident or transient flora. Objectives: The aim of our study was to perform the phenotypic and genotypic characterization of culturable Candida isolates present in stool specimens of healthy Tunisian individuals and to evaluate their antifungal susceptibility. Methods: Yeasts were recovered from 46 stool samples cultured on Sabouraud dextrose agar at 37°C. Species were identified using conventional methods and ITS-PCR sequencing. Candida isolates were tested by exploring their tolerance to oxidative stress and extreme acidic conditions. In addition, their biofilm formation ability and in vitro resistance to antifungals was determined by the VITEK 2 system. Results: The identification by sequencing the ITS1-5.8S-ITS2 region of the 56 yeast strains isolated from 37 stool samples revealed that Candida was the dominant genus and was represented by Candida albicans (n = 21), C. parapsilosis (n = 10), C. glabrata (n = 9), and C. krusei (n = 9). In contrast, the other genera, including Trichosporon, Geotrichum, and Rhodotorula, were sporadically occurring. We found that most Candida isolates were able to form biofilms under oxidative stress and extreme pH conditions. Regarding antifungal susceptibility, a higher resistance rate to fluconazole was revealed in comparison to caspofungin and micafungin. However, no resistance was revealed against voriconazole, amphotericin B, and 5-flucytosine. Conclusions: This is the first work-generated data on cultivable yeasts from stool specimens of healthy individuals in Tunisia. Further metagenomic studies with a larger sample size are needed to better characterize the intestinal mycobiota.