UV or PAA for Wastewater Disinfection: a Comparison of the Impact on Virulence Genes

摘要

Ultraviolet (UV) and peracetic acid (PAA) disinfection have been used in municipal wastewaterrntreatment plants (WWTPs) for their biocidal effect on microorganisms. The current study usedrnPCR-Bioplex and DNA microarray genotyping techniques to investigate the impact of UV andrnPAA on the change in frequency of virulence genes in E. coli isolates and on the prevalence ofrnuropathogenic E. coli (UPEC) isolates in wastewater effluents. Effluents from four WWTPsrn(activated sludge [AS], biofiltration [BF] and physicochemical [PC1 and PC2]) located inrnQuébec, Canada, were sampled before disinfection and exposed to UV or PAA doses in the labrnto reach a target count of approximately 200 CFU/100 mL. To achieve this, the required UVrnfluences ranged between 7 – 30 mJ/cm2, depending on the plant, while the PAA dose variedrnbetween 0.9 – 2.0 mg/L. E. coli isolates totaling 1,766 were extracted from the samples pre- andrnpost- disinfection, then screened by PCR/Bioplex to detect those likely to be UPECs, using threernvirulence genes (hlyA, papC and cnf1). The UPEC pathotypes of the positively screened isolatesrnwere confirmed by microarrays. The proportion of UPEC isolates decreased in all samples afterrndisinfection, with that due to UV varying between 22% ? 80%, and the reduction due to PAArnranging between 11% ? 100%. The average reductions by UV (55%) and PAA (52%) werernstatistically significant (P<0.05). Gene frequency analysis revealed that the decline in thernpopulation of UPEC pathotypes by UV or PAA was not linked to specific virulence factors asrnmost virulence genes were lost, suggesting that entire pathogenicity islands (PAIs), carryingrnclusters of virulence genes, were lost through disinfection. Thus, this study showed that both UVrnand PAA disinfection appear to significantly reduce the proportions of UPECs in the survivingrnE. coli populations in wastewater effluents.