Wastewater as a Probable Environmental Reservoir of Extended-Spectrum-β-Lactamase Genes: Detection of Chimeric β-Lactamases CTX-M-64 and CTX-M-123

Global spread of CTX-M-type extended-spectrum β-lactamase (ESBL)-producingEnterobacteriaceae is a critical concern in both clinical and community settings. This dominance of CTX-M-type ESBL producers may be largely due to the successful international spread of epidemic clones, as represented by the extraintestinal pathogenicEscherichia coli (ExPEC) ST131. Our findings highlight the worrisome presence of diverseE. coli clones associated with humans, including ExPEC lineages harboring the most commonbla CTX-M variants in untreated wastewater samples. Moreover, the chimeric genesbla CTX-M-64 andbla CTX-M-123 , which have not yet been identified from human isolates of domestic origin in Japan, were identified. Exposure to untreated wastewater through combined sewer overflow caused by heavy rains derived from abnormal weather change could pose a risk for human health due to ingesting those antimicrobial-resistant bacteria.