Abstract
The influence of nutrients in wastewater from dairy lagoons on the survival of Escherichia coli O157:H7 was monitored. Initially, the survival of E. coli O157:H7 in wastewater from which the competing native organisms had been removed by filter sterilization or autoclaving was compared with that in wastewater from which competing organisms had not been removed. Numbers of E. coli O157:H7 or E. coli ONT (O-nontypeable):H32 cells declined rapidly in filter-sterilized water and exhibited a slower decline in nonsterile water, while the organisms proliferated in autoclaved water. Subsequently, the growth of E. coli O157:H7 strains was monitored in 300 mul of Luria-Bertani (LB) broth supplemented with incremental proportions of filter-sterilized wastewater. E. coli O157:H7 and E. coli ONT:H32 strains failed to grow in filter-sterilized wastewater, and their growth was reduced incrementally with wastewater supplementation of LB broth. Consequently, the influence of organic extracts of wastewater on the growth of E. coli O157:H7 and E. coli ONT:H32 in reduced-strength LB was monitored, followed by scale-up tests in wastewater. Acidic and basic extracts inhibited growth of both strains, while the neutral aqueous extract improved growth. However, a scale-up with a threefold increase in the acidic components supplementing the wastewater did not result in any additional decline in numbers of E. coli O157:H7 cells. When protected inside a 300-kDa dialysis tube and exposed to diffusible components, E. coli O157:H7 survived longer, with a decimal reduction time of 18.1 days, compared to 3.5 days when inoculated directly into wastewater. Although wastewater can potentially provide nutrients to naturally occurring human pathogens, the chemical components, protozoa, and coliphages in wastewater can inhibit the growth of freshly introduced pathogens from manure.