Diversity and antifungal susceptibility yeast in the selected rivers in the North West Province
Monapathi, Mzimkhulu Ephraim
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Several yeast species had previously been isolated from water systems in the North West Province, South Africa. Some of the identified species had, in other studies, been associated with superficial mucosal infections to life threatening diseases. Antifungal drugs are used to treat such yeast infections. However, due to prophylactic usage and continuous exposure some yeast species have developed resistance to some antifungal agents. The aim of this study was to determine the diversity and antifungal susceptibility of yeasts in selected rivers, Mooi River and Harts River in the North West Province, South Africa. Waters samples were collected from the rivers in summer and winter seasons. Physico-chemical parameters such as pH, temperature, total dissolved solids, chemical oxygen demand, nitrates and phosphates were measured to determine the water quality. Yeast colonies were enumerated at room temperature and 37°C using yeast-malt-extract agar (containing 100 ppm chloramphenicol). Pure isolates from 37°C were identified by biochemical tests and 26S rRNA gene sequencing. Yeast sequences of isolated yeasts were sent to Genbank. Phylogenetic tree was conducted to determine phylogenetic relationship between the yeast isolates. Disk diffusion antifungal susceptibility tests were conducted on the yeast species. Physico-chemical parameters of the water were within target water quality range for livestock farming but in most sampling sites out of range for irrigation use. pH, Nitrates, phosphates and chemical oxygen demand levels ranged from 7.40 to 8.64, 0 to 5.4 mg/L, 0 to 7.14 mg/L and 31 to 43 mg/L, respectively. Elevated levels of total dissolved solids were measured in all the sampling sites. Total yeast counts ranged between 320-4200 cfu/L and 27-2573 cfu/L for room temperature and 37˚C. All the yeast colonies isolated were non-pigmented. Diazonium Blue B tests determined the yeasts isolates as ascomycetes. Haemolysin and extracellular enzyme production tests were negative on all the isolates. Yeasts isolates were identified and belonged to the genera Arxiozyma, Candida, Clavispora, Cyberlindnera, Lecythophora, Pichia, Saccharomyces, and Wickerhamomyces. Saccharomyces cerevisiae and Candida glabrata were mostly isolated species. Furthermore, the results indicated that levels of yeast could be correlated to physico-chemical quality of water. A large number of isolates were resistant to azoles, especially fluconazole as well as other antifungal classes. Most of the Candida species were resistant to almost all the antifungals. Several of the isolated yeast species are opportunistic pathogens. They could cause infections in sensitive individuals during occasional direct contact especially immune compromised people. Resistance of these yeast species to antifungal agents is a major health concern.