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Antibiotic-resistant bacteria mirror the behaviour of faecal indicators during municipal wastewater treatment and discharge

Journal Article (2025)
Author(s)

B. Bicudo (Unicef, TU Delft - Sanitary Engineering)

Doris Van Halem (TU Delft - Sanitary Engineering)

G Medema (Michigan State University, TU Delft - Water Systems Engineering, KWR Water Research Institute)

Research Group
Sanitary Engineering
DOI related publication
https://doi.org/10.2166/washdev.2025.094
More Info
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Publication Year
2025
Language
English
Research Group
Sanitary Engineering
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Abstract

Classic faecal indicators, Escherichia coli and intestinal enterococci, were investigated as prospective proxies for presence of their resistant strains Extended Spectrum Betalactamase-producing (ESBL)-E. coli and Vancomycin Resistant Enterococci (VRE). These organisms are of global public health concern, and their tracing in water treatment systems is not yet standard practice. In this study, no significant difference was observed in the behaviour of the resistant bacteria and their sensitive counterparts during activated sludge treatment, chlorination, electrocoagulation and natural decay. Activated sludge treatment provided a 2.23 ± 0.13 log reduction value (LRV) for antibiotic resistant and sensitive bacteria alike. Disinfection by both free chlorine and electrocoagulation was slightly more effective against E. coli and ESBL-E. coli than against enterococci and VRE, though no significant difference was observed between the resistant bacteria and their sensitive counterparts. Decay experiments at 4, 13 and 24 °C showed a biphasic behaviour, with no relevant difference in decay between either of the indicators. It is therefore concluded that antibiotic-resistant ESBL-E. coli and VRE mirror the behaviour of faecal indicators E. coli and enterococci, experiencing the same rates of disinfection/decay, and maintaining similar ratios between sensitive and resistant populations before and after treatment.