Impact of UV and peracetic acid disinfection on the prevalence of virulence and antimicrobial resistance genes in uropathogenic Escherichia coli in wastewater effluents

Abstract

Wastewater discharges may increase the populations of pathogens, including Escherichia coli, and of antimicrobial-resistant strains in receiving waters. This study investigated the impact of UV and peracetic acid (PAA) disinfection on the prevalence of virulence and antimicrobial resistance genes in uropathogenic Escherichia coli (UPEC), the most abundant E. coli pathotype in municipal wastewaters. Laboratory disinfection experiments were conducted on wastewater treated by physicochemical, activated sludge, or biofiltration processes; 1,766 E. coli isolates were obtained for the evaluation. The target disinfection level was 200 CFU/100 ml, resulting in UV and PAA doses of 7 to 30 mJ/cm(2) and 0.9 to 2.0 mg/liter, respectively. The proportions of UPECs were reduced in all samples after disinfection, with an average reduction by UV of 55% (range, 22% to 80%) and by PAA of 52% (range, 11% to 100%). Analysis of urovirulence genes revealed that the decline in the UPEC populations was not associated with any particular virulence factor. A positive association was found between the occurrence of urovirulence and antimicrobial resistance genes (ARGs). However, the changes in the prevalence of ARGs in potential UPECs were different following disinfection, i.e., UV appears to have had no effect, while PAA significantly reduced the ARG levels. Thus, this study showed that both UV and PAA disinfections reduced the proportion of UPECs and that PAA disinfection also reduced the proportion of antimicrobial resistance gene-carrying UPEC pathotypes in municipal wastewaters.

FIG 1

Effects of UV(a) and PAA (b). E. coli inactivation curves for nonfiltered (NF) samples from activated sludge (AS), biofiltration (BF1), and physicochemical (PC1) treatment plants. PAA contact time (T) was 30 min except for BF2 samples. The effect of particles on the inactivation kinetics was tested for UV on the PC2 plant samples (a) and for PAA on the BF2 plant samples (b); in both cases, nonfiltered (NF) can be compared to filtered (F) samples. The PAA contact time for BF2 was increased to 60 min for these experiments because of high consumption of PAA. Data points circled are those conditions for which E. coli isolation was done.

FIG 2

Prevalence of uropathogenic E. coli (UPEC) in nondisinfected (ND; open bars) and disinfected (D; gray bars) effluent samples of activated sludge (AS), biofiltration (BF1 and BF2), and physicochemical (PC1 and PC2) plants by UV (a) and PAA (b). Error bars are the standard errors as calculated using the log-linear model. The number in parentheses above each bar represents the total number of isolates screened by PCR/Bioplex.

FIG 3

Pathotype (UPEC, uropathogens; OP, other pathotypes; NP, nonpathogenic) and phylotype (A, gray bars; B1, hatched bars; B2, open bars; D, black bars) distribution of the 323 screen-positive E. coli isolates and 169 nonscreened (i.e., directly pathotyped by microarrays) E. coli isolates. n, number of isolates in each category.

FIG 4

Prevalence of uropathogenic E. coli (UPEC) pathogenicity islands (PAIs) in a total of 323 screen-positive E. coli isolates (non-UPEC, 209 isolates, open bars; UPEC, 114 isolates, gray bars).

FIG 5

Changes of the prevalence of uropathogenic E. coli (UPEC) virulence genes in each virulence factor by UV (open bars) and PAA (gray bars). A positive log-odds ratio means an increase in the relative frequency of a group of virulence genes upon disinfection. Error bars are the standard errors calculated using the log-linear model.

FIG 6

Co-occurrence of virulence and antimicrobial resistance genotypes. (a) Average antimicrobial resistance gene classes in nonuropathogenic E. coli (non-UPECs) and uropathogenic E. coli (UPECs). (b) Prevalence of antimicrobial resistance gene-carrying E. coli in non-UPECs and UPECs. Significant occurrences are indicated by an asterisk.