Seasonal abundance and distribution of Vibrio species in the treated effluent of wastewater treatment facilities in suburban and urban communities of Eastern Cape Province, South Africa

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 × 10(5) to 4.36 × 10(4) CFU/ml in the suburban community and from 2.80 × 10(5) to 1.80 × 10(5) CFU/ml in the urban community. Vibrio species associated with 180 μ, 60 μ, and 20 μ plankton sizes were observed at densities of 0-136 × 10(3) CFU/ml, 0-8.40 × 10(2) CFU/ml, and 0-6.80 × 10(2) CFU/ml, respectively at the suburban community's WWTP. In the urban community, observed densities of culturable Vibrio were 0-2.80 × 10(2) CFU/ml (180 μ), 0-6.60 × 10(2) CFU/ml (60 μm), and 0-1.80 × 10(3) CFU/ml (20 μm). The abundance of free-living Vibrio species ranged from 0 to 1.0 × 10(2) and 1.0 × 10(3) 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 plankton-associated 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.