Virulence gene profiling and cytotoxicity of <i>Vibrio</i> spp. isolated from treated wastewater effluent and receiving surface waters in Durban, South Africa

Untreated or partially treated wastewater often harbours virulent <i>Vibrio</i> species that threaten environmental and public health. This study aimed to characterize the virulence gene profiles and cytotoxic effects of <i>Vibrio</i> species isolated from treated effluents and downstream rivers at four wastewater facilities in Durban, KwaZulu-Natal province, South Africa. A total of 200 <i>Vibrio</i> spp., isolated from treated effluent and surface waters of four wastewater treatment facilities in Durban, KwaZulu-Natal, were screened, with <i>Vibrio vulnificus</i> isolates (<i>n</i> = 178) showing high prevalence of iron acquisition genes such as <i>viuB</i> (72.47%), <i>feoB</i> (56.74%) and <i>fbpC</i> (55.06%) while other virulence genes like <i>ompU</i>, <i>apxIB</i>, and <i>hlyB</i> were also detected. <i>Vibrio alginolyticus</i> isolates (<i>n</i> = 15) exhibited <i>rtx</i> (66.67%) and <i>pvuA</i> (46.67%), among others. Five representative isolates caused a progressive decline in cell viability in both HepG2 and HEK293 cells over 72 h, with final viability dropping below 3% in multiple instances. Morphological damage confirmed strong cytotoxic activity. Statistical analysis showed significant associations between specific genes detected among the isolates. These findings demonstrate that treated wastewater still contains highly virulent <i>Vibrio</i> strains capable of harming human cells, posing ongoing risks in regions with compromised water infrastructure.