Quantitative study of ESBL and carbapenemase producers in wastewater treatment plants in Seville, Spain: a culture-based detection analysis of raw and treated water

Antibiotics can modify populations of multidrug-resistant microorganism (MDRO) in urban wastewater. Our objectives were to quantify the differences in MDR Gram-negative bacteria between influents and effluents of WWTPs of a Spanish city and to evaluate the influence of human antibiotic prescriptions, as well as the persistence of these bacteria after treatment and their genetic relatedness to clinical isolates. The mean count of ESBL producers and carbapenemase producers were 3.77 and 2.74 log 10 CFU/ml, respectively. The reduction achieved by water treatment of ESBL-producing organisms was 1.4-log (96.11 %), whereas a 1.8-log reduction (98.36 %) was obtained regarding carbapenemase producing organisms. Aeromonas spp. predominated among MDROs and bla_KPC-2 was the main carbapenemase detected in the influent wastewater samples. Among Escherichia coli and Klebsiella pneumoniae influent isolates, 44 % and 30 %, respectively, belonged to high-risk clones. Regarding Enterobacteriaceae, 10.6 % matched clinical isolates and one strain from an ongoing hospital outbreak was identified among raw samples. New MDROs and persistence of certain strains were detected in effluent samples. Quinolone and third-generation cephalosporin prescriptions, flow rate and population density were associated with higher OXA-48 producer counts. Despite reductions, additional technologies should be implemented in WWTPs receiving hospital discharges. Given the prevalence of environmental species, culture-based and metagenomic approaches should be combined to distinguish between human and sewage sources for antibiotic resistance monitoring. Overall, this study shows that WWTPs with secondary treatment are effective at removing MDRO, and antibiotic stewardship is a potential strategy to reduce the release of MDROs.