An analysis of municipal and hospital wastewater in Japan found a high number of multidrug-resistant Escherichia coli strains, with significantly more found in the municipal wastewater, researchers reported last week in the Journal of Global Antimicrobial Resistance.
In the study, researchers with Yamagata University and Tohuko University School of Medicine sampled wastewater from a municipal wastewater treatment plant and a hospital in the city of Sendai twice a month from February 2019 to February 2020.
Over the study period, 279 and 37 strains of ESBL-EC were isolated from municipal and hospital wastewater, respectively.
A previous study by the group in the same city had detected higher levels of antibiotic-resistant bacteria (ARB) in municipal wastewater than hospital wastewater, which demonstrated the feasibility of using municipal wastewater to monitor for ARB in healthy populations.
The aim of this study was to investigate the levels of extended-spectrum beta-lactamase–producing E coli (ESBL-EC) in the wastewater and to further characterize the isolated strains of ESBL-EC using antibiotic susceptibility testing and multi-locus sequence typing (MLST).
Over the study period, 279 and 37 strains of ESBL-EC were isolated from municipal and hospital wastewater, respectively. All 316 isolates were resistant to ampicillin and cefotaxime and susceptible to imipenem and tigecycline, and 98.1% possessed blaCTX-M genes, with blaCTX-M-9 detected most frequently (62.3%). Six isolates from municipal wastewater and one from hospital wastewater contained multiple blaCTX-M genes.
MLST revealed a higher diversity of sequence types (STs) in isolates from the municipal wastewater than in those from the hospital wastewater, but E coli ST131—an epidemic ESBL-EC strain that has caused multidrug-resistant urinary tract infections worldwide—was the most common ST in both types of wastewater.
"These results support our hypothesis that monitoring municipal wastewater can effectively obtain comprehensive information about the strains of this clinically important ARB circulating in the study area, some of which may cause human infections in the future," the study authors wrote.