Water quality and antifungal resistance of yeast species from selected rivers in the North West Province
Monapathi, Mzimkhulu Ephraim
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The present study focused on the diversity and characteristics of yeasts present in North West Province (NWP) surface water as well as antifungal agents and associated resistance. The first part of this study is a review that addressed the diversity, significance and health implication of aquatic yeasts. The review highlighted the presence of diverse yeast species in aquatic environments. It detailed characteristics of yeasts which could be beneficial or detrimental in human, plants and animals. A gap in research between clinical isolates, known pathogens, and environmental isolates was emphasized. This is vital as some studies have shown similar phylogenetic relationships between clinical and environmental isolates. In the second part of the study, the application of yeasts as water quality indicators was discussed. From four selected rivers in the NWP, significant differences in physico-chemical and microbiological parameters were observed seasonally as well as between the rivers systems. Furthermore, an association was observed between some physico-chemical parameters and yeast levels. High nutrient load, chemical oxygen demand and dissolved oxygen indicated eutrophication conditions in these river systems. Some studies have also associated high levels of yeasts and certain yeasts species with faecal contaminated water. Pathogenic yeasts were resistant to various antifungal agents. In the third part of the study, efflux pump genes (CDR1, CDR2, FLU1 and MDR1) coding for resistance to fluconazole were detected in environmental Candida albicans isolated from the water resources. The sequences of these genes were phylogenetically similar to those from clinical origin. These findings were worrisome since C. albicans is an opportunistic pathogen that causes most infections in human immunodeficiency virus (HIV) patients and fluconazole is the most used antifungal agents in HIV treatment. The fourth part of the study addressed pollution from pharmaceutical products and yeasts in water. Yeast levels were determined from copy numbers of 26S rRNA genes in environmental DNA and were quantified by qPCR. Commonly used antifungal agents were also quantified and screened for. The study provided an insight into yeast levels determined by rapid DNA extraction and a culture independent approach. Furthermore, antifungal agents were detected and fluconazole levels quantified. The information generated in this study demonstrated association of yeast levels to polluted water as indicated by physico-chemical parameters. Antifungal resistance among pathogenic yeasts as well as mechanisms of resistance was demonstrated. Additionally, the presence and levels of antifungal agents suggested that selection and maintenance of antifungal resistant yeasts occur in aquatic ecosystems. In general, the results from the present study will be valuable in understanding the impact of pathogenic yeasts in aquatic systems. It will be beneficial in making policies for ensuring that mitigation strategies are put in place to prevent spread of antifungal resistance from clinical to aquatic environments. The outcome from the results will contribute towards improved antifungal therapy and development of new strategies against antifungal resistance.