Impact of wastewater treatment processes on antimicrobial resistance genes and their co-occurrence with virulence genes in Escherichia coli

- Activated sludge increased the prevalence of resistance genes in Escherichia coli.
- Physicochemical systems reduced the prevalence of resistance genes in E. coli.
- Main detected resistance genes: aminoglycoside, β-lactam, quinolone and tetracycline.
- E. coli containing multiple resistance genes contained insertion sequence elements.
- A positive co-occurrence was observed between resistance and virulence genes.

An increase in the frequency of antimicrobial resistance genes (ARGs) in bacteria including Escherichia coli could be a threat to public health. This study investigated the impact of activated sludge and physicochemical wastewater treatment processes on the prevalence of ARGs in E. coli isolates. In total, 719 E. coli were isolated from the influent and effluent (prior to disinfection) of two activated sludge and two physicochemical municipal treatment plants, and genotyped using DNA microarrays. Changes in the abundance of ARGs in the E. coli population were different for the two treatment processes. Activated sludge treatment did not change the prevalence of ARG-possessing E. coli but increased the abundance of ARGs in the E. coli genome while physicochemical treatment reduced both the prevalence of ARG-carrying E. coli as well as the frequency of ARGs in the E. coli genome. Most E. coli isolates from the four treatment plants possessed ARGs of multiple antimicrobial classes, mainly aminoglycoside, β-lactams, quinolone and tetracyclines. In addition these isolates harboured DNA insertion sequence elements including integrase and transposase. A significant positive association was found between the occurrence of ARGs and virulence genotypes.

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