Investigating an emerging menace in groundwater sources: the occurrence, antifungal resistance phenotypes, and virulence potential of yeast contaminants

Groundwater is an important resource where potable pipe-borne water is lacking. Albeit, yeast-contaminated water is an emerging threat posing a severe risk to public health. This study investigated the occurrence, drug-resistance profile, and virulence potential of yeasts isolated from groundwater sources. Grab groundwater samples were obtained during arid and wet periods, and analysed for yeast enumeration and isolation following standard protocols. The isolates were characterized using phenotypic and molecular approaches and assessed for antibiotic resistance employing standard antifungal agents. Biofilm formation and enzymatic activities including phospholipase, proteinase, lipase, and haemolysin were evaluated. Yeast counts were between 0 and 4 CFU/mL, across both seasons, and 52 yeasts were recovered. The identification and the occurrence of the yeasts were as follows: Candida orthopsilosis (28, 53.8%), Cutaneotrichosporon curvatum (12, 23.1%), Pichia guilliermondii (4, 7.7%), and Pichia kudriavzevii (8, 15.4%). Resistance profile of the isolates was fluconazole (12, 92.30%), flucytosine and amphotericin B (9, 69.23%), and ketoconazole (6, 46.15%). Thirty (30, 58%) isolates were multidrug-resistant, with the highest MARP, 4 (KCA-FLU-AFY-AMB), obtained across the samples. MARI was between 0.75 and 1.00, suggesting the isolates were from sources where antifungals were frequently used. All the isolates were weak biofilm producers, also some showed activity for the hydrolytic enzyme studied. Findings from this study highlight the need for effective monitoring of yeast contamination and antifungal surveillance in groundwater sources. Proper treatment of groundwater is also essential for quality and safe human consumption. A higher number of yeasts contaminants were recorded in the arid season compared to the wet season. A significant proportion, specifically 30 (58%) of the yeast isolates were multidrug-resistant. The isolates have virulence factors that could exacerbate disease severity in susceptible hosts. Monitoring groundwater yeast contaminants, antifungal resistance, and virulence is key for public health.