Prevalence and distribution of Listeria pathogens in the final effluents of a rural wastewater treatment facility in the Eastern Cape Province of South Africa

We assessed the prevalence of free-living and plankton-associated Listeria species in the final effluents of a South African wastewater treatment facility and its receiving watershed between August 2007 and July 2008 as well as the antibiotic susceptibilities of effluent isolates. The physicochemical quality of the raw sewage and treated effluents was also determined. Free-living Listeria were more prevalent (96%), compared to plankton-associated Listeria species (58-67%). Listeria pathogens were sensitive to 11 (55%) of the 20 tested antibiotics, and showed varying (7-71%) levels of resistance to eight antibiotics. Turbidity, COD, NO3, PO4 and Listeria density fell short of recommended standards after treatment; while pH, temperature, TDS, DO and NO2 were compliant with target quality after treatment. We conclude that final effluents of wastewater treatment plants are potential sources of Listeria pathogens in the aquatic milieu of South Africa.