Biological and Physicochemical Wastewater Treatment Processes Reduce the Prevalence of Virulent Escherichia coli

Abstract

bEffluents discharged from wastewater treatment plants are possible sources of pathogenic bacteria, including Escherichia coli, in the freshwater environment, and determining the possible selection of pathogens is important. This study evaluated the impact of activated sludge and physicochemical wastewater treatment processes on the prevalence of potentially virulent E. coli. A total of 719 E. coli isolates collected from four municipal plants in Québec before and after treatment were characterized by using a customized DNA microarray to determine the impact of treatment processes on the frequency of specific pathotypes and virulence genes. The percentages of potentially pathogenic E. coli isolates in the plant influents varied between 26 and 51%, and in the effluents, the percentages were 14 to 31%, for a reduction observed at all plants ranging between 14 and 45%. Pathotypes associated with extraintestinal pathogenic E. coli (ExPEC) were the most abundant at three of the four plants and represented 24% of all isolates, while intestinal pathogenic E. coli pathotypes (IPEC) represented 10% of the isolates. At the plant where ExPEC isolates were not the most abundant, a large number of isolates were classified as both ExPEC and IPEC; overall, 6% of the isolates were classified in both groups, with the majority being from the same plant. The reduction of the proportion of pathogenic E. coli could not be explained by the preferential loss of one virulence gene or one type of virulence factor; however, the quinolone resistance gene (qnrS) appears to enhance the loss of virulence genes, suggesting a mechanism involving the loss of pathogenicity islands.

Impact of UV and Peracetic Acid Disinfection on the Prevalence of Virulence and Antimicrobial Resistance Genes in Uropathogenic Escherichia coli in Wastewater Effluents

“…DNA microarrays used in this study contained 306 probes (70-mers) targeting different versions of 195 virulence and virulence-related genes, 70 antimicrobial resistance genes of 11 classes including genes encoding aminoglycoside, beta-lactam, macrolide, olaquindox, phenicol, quaternary ammonium compounds, quinolone, rifampin, sulfonamides, tetracyclines, trimethoprim, and 8 genes encoding mobile genetic elements (13,17,29,48). The full list of virulence genes with their probes and pathotype classification rules was presented previously (29,48). The description of antimicrobial resistance genes and mobile genetic element markers is reported by Biswal et al (13); however, their probes are published elsewhere (48).…”

“…Inducing these two gene classes can lead to the excision of certain unstable pathogenicity islands in various species (34)(35)(36). Consequently, the "neutralization" of a pathogenic strain is not necessarily the result of complete inactivation of this strain but can also be due to the deletion of certain virulence genes by pathogenicity island excision, thus rendering the strain nonpathogenic (29). This mechanism has been demonstrated specifically for unstable UPEC pathogenicity islands that were lost upon exposure to quinolones (causing DNA strand breaks by inhibiting gyrase activity) or other environmental stresses (36,37).…”

“…Previous studies have used genotyping methods for detecting virulence genes using PCR (26,27), colony hybridization (28), and genomic DNA microarray hybridization in order to identify pathogenic E. coli (17,(29)(30)(31). All have found ExPECs and often specifically UPECs to be the predominant pathotypes in both natural waters and municipal wastewaters, while IPECs were present either sporadically or most often at low levels.…”

Ecological and Public Health Implications of the Discharge of Multidrug-Resistant Bacteria and Physicochemical Contaminants from Treated Wastewater Effluents in the Eastern Cape, South Africa

“…Human and animal fecal matters from wastewater are major sources of enteropathogenic microbes in freshwater environments [4]. Numerous species of enteric pathogens capable of causing viral, bacterial and parasitic infections may be present in environmental water, including discharged wastewater effluents, and at least one novel enteric pathogen has been discovered each year over the past decades [5].…”

Photochemical treatment as an alternative to improve the quality of wastewater after advanced primary treatment.

“…When water is treated with ultraviolet light, the microorganism die or had been temporary inactivated, if the light exposition time is not sufficient, it is possible that the microorganism find again the adequate conditions for their grown and multiplication. Some microorganisms are pathogenic and cause diseases in general are bacteria, viruses, protozoa and worms from domestic sewage and decomposition of animal wastes [11][12][13][14][15] .…”