Abstract

We assessed the seasonal abundance and distribution of Vibrio species as well as some selected environmental parameters in the treated effluents of two wastewater treatment plants (WWTP), one each located in a suburban and urban community of Eastern Cape Province, South Africa. Vibrio population density ranged from 2.1×101 to 4.36×104 CFU/ml in the suburban community and from 2.80×101 to 1.80×105 CFU/ml in the urban community. Vibrio species associated with 180 μm, 60 μm, and 20 μm plankton sizes were observed at densities of 0-1.36×103 CFU/ml, 0-8.40×102 CFU/ml, and 0-6.80×102 CFU/ml, respectively at the suburban community’s WWTP. In the urban community, observed densities of culturable Vibrio were 0-2.80×102 CFU/ml (180 μm), 0-6.60×102 CFU/ml (60 μm), and 0-1.80×103 CFU/ml (20 μm). The abundance of free-living Vibrio species ranged from 0 to 1.0×102 and 1.0×103 CFU/ml in the suburban and urban communities’ WWTPs, respectively. Molecular confirmation of the presumptive Vibrio isolates revealed the presence of V. fluvialis (41.38%), V. vulnificus (34.48%), and V. parahaemolyticus (24.14%) in the suburban community effluents. In the urban community molecular confirmation revealed that the same species were present at slightly different percentages, V. fluvialis (40%), V. vulnificus (36%), and V. parahaemolyticus (24%). There was no significant correlation between Vibrio abundance and season, either as free-living or planktonassociated entities, but Vibrio species abundance was positively correlated with temperature (r=0.565; p<0.01), salinity, and dissolved oxygen (p<0.05). Turbidity and pH showed significant seasonal variation (p<0.05) across the seasons in both locations. This study underscores the potential of WWTPs to be sources of Vibrio pathogens in the watershed of suburban and urban communities in South Africa.

• Keywords: environmental parameters; public health; Vibrio pathogens; treated effluents