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

The presence of antimicrobial-resistant bacteria and resistance genes in aquatic environments is a serious public health concern. This study focused on Escherichia coli possessing bla(CTX-M) genes in wastewater inflows. Twelve crude inflow water samples from wastewater treatment plant (WWTP) A and two samples each from three other WWTPs were collected in 2017 and 2018. A total of 73 E. coli isolates with 31 different sequence types (STs) harboring distinctive bla(CTX-M) gene repertoires were detected. In WWTP A influents, bla(CTX-M-14) (14 isolates) was dominant, followed by bla(CTX-M-15 )(12 isolates) and bla(CTX-M-27) (10 isolates). The chimeric bla(CTX-M-)(64) and bla(CTX-M-123) genes were each identified in one of the E. coli isolates from the same WWTP A inflow port. The bla(CTX-M-27) gene was associated with five of seven B2-ST131 isolates, including three isolates of the B2-O25b-ST131-H30R/non-Rx lineage. One of the remaining two isolates belonged to the B2-O25b-ST131-H30R/Rx lineage harboring the bla(CTX-M-15) gene. As for the B2-025b-ST131-H30R/non-Rx lineage, two isolates with bla(CTX-M-27) were recovered from each of the WWTP B and D influents, and one isolate with bla(CTX-M-174) was also recovered from WWTP B influent. Whole-genome sequencing of chimeric bla(CTX-M) -harboring E. coli isolates revealed that the bla(CTX-M-64) gene was integrated into the chromosome of ST10 E. coli B22 via ISEcp1-mediated transposition of a 9,467-bp sequence. The bla(CTX-M-123)-carrying Incl1 plasmid pB64 was 109,169 bp in length with pST108. The overall findings suggest that wastewater may act as a probable reservoir of clinically significant clonal lineages mediating antimicrobial resistance genes and chimeric genes that have not yet been identified from human isolates of domestic origin in Japan.
Article
Applied and Environmental Microbiology 85(22) : e01740-19-(2019)