Characterization of NDM-5- and CTX-M-55-coproducing GSH8M-2 Isolated from the Effluent of a Wastewater Treatment Plant in Tokyo Bay

Purpose: New Delhi metallo-β-lactamase (NDM)-5-producing Enterobacteriaceae have been detected in rivers, sewage, and effluents from wastewater treatment plants (WWTPs). Environmental contamination due to discharged effluents is of particular concern as NDM variants may be released into waterways, thereby posing a risk to humans. In this study, we collected effluent samples from a WWTP discharged into a canal in Tokyo Bay, Japan.

Methods: Testing included the complete genome sequencing of GSH8M-2 isolated from the effluent as well as a gene network analysis.

Results: The complete genome sequencing of GSH8M-2 revealed that it was an NDM-5-producing strain sequence type ST542, which carries multiple antimicrobial resistance genes for β-lactams, quinolone, tetracycline, trimethoprim-sulfamethoxazole, florfenicol/chloramphenicol, kanamycin, and fosfomycin. The gene was found in the IncX3 replicon plasmid pGSH8M-2-4. Gene network analysis using 142 IncX3 plasmid sequences suggested that pGSH8M-2-4 is related to both clinical isolates of   and species in Eastern Asia. GSH8M-2 also carries the gene in IncX1 plasmid pGSH8M-2-3.

Conclusion: This is the first report of environmental NDM-5-producing isolated from a WWTP in Japan. NDM-5 detection is markedly increasing in veterinary and clinical settings, suggesting that dual β-lactamases, such as NDM-5 and CTX-M-55, might be acquired through multiple steps in environment settings. Environmental contamination through WWTP effluents that contain producers of NDM variants could be an emerging potential health hazard. Thus, regular monitoring of WWTP effluents is important for the detection of antimicrobial-resistant bacteria that may be released into the waterways and nearby communities.