Distribution and Public Health Significance of Vibrio Pathogens Recovered from Selected Treated Effluents in the Eastern Cape Province, South Africa

Treated sewage harbours pathogenic microbes, such as enteric bacteria and protozoa, are capable of causing several diseases. Some of these are emerging pathogens sometimes recovered in the absence of common water quality indicator organisms. The possibility of selected treatments plants serving as momentary reservoirs of Vibrio pathogens during a non-outbreak period was assessed. The occurrence and diversity of Vibrio pathogens were monitored for one year (December 2016 to November 2017) in the treated effluents and upstream and downstream areas of the receiving water bodies of two wastewater treatment plants (WWTPs), designated AL and TS. Physicochemical parameters of TS and AL WWTPs’ water samples were analysed using a multi-parameter meter (Hanna, model HI 9828, Padova, Italy) and a turbidimeter (HACH, model 2100P, Johannesburg, South Africa). Water samples were augmented with alkaline peptone water and cultured on thiosulfate citrate bile salts sucrose agar at 37 °C for 24 h. The recovered probable pathogens were confirmed via PCR amplification, using primers specific for Vibrio species of public health significance. The distribution of Vibrio species positively and significantly (p < 0.01) correlated with turbidity (r = 0.630), temperature (r = 0.615), dissolved oxygen (r = 0.615), pH (r = 0.607), biological oxygen demand (r = 0.573), total dissolved solid (r = 0.543), total suspended solid (r = 0.511), electrical conductivity (r = 0.499), residual chlorine (r = 0.463) and salinity (r = 0.459). The densities of Vibrio species were found to be significantly higher (p < 0.05) in effluents from both AL and TS WWTPs than upstream and downstream of the receiving rivers across the sampling regime. Furthermore, the maximum Vibrio species density across the sampling regime were observed during the warmer Summer and Spring season. Moreover, six medically important Vibrio species were detected in the water samples, indicating that the methods employed were efficient in revealing that WWTPs are potential reservoirs of Vibrio pathogens, which could pose a substantial public health risk if the receiving water is used for domestic purposes. Our findings further strengthen existing calls for the inclusion of emerging bacterial pathogens, including Vibrio species, as water quality indicators by the South African Department of Water Affairs. Hence, we recommend regular monitoring of treated effluents and receiving water bodies to ensure early control of potential outbreaks of vibriosis and cholera.