Surface water is suspected of playing a role in the development and spread of antimicrobial-resistant (AR) bacteria, including human pathogens. In our previous study, 496 Escherichia coli isolates were recovered from water samples collected over a 2-year period from the Upper Oconee watershed, Athens, GA, United States, of which 34 (6.9%) were AR isolates. Of these, six isolates were selected based on their multidrug resistance (MDR) phenotypes, the presence of mobile genetic elements, and their pathogenic potential and were subjected to whole-genome sequence (WGS) analysis to enhance our understanding of environmental MDR E. coli isolates. This study is the first report on genomic characterization of MDR E. coli from environmental water in the United States through a WGS approach. The sequences of the six MDR E. coli isolates were analyzed and the locations of their AR genes were identified. One of the E. coli isolates was an ST131 epidemic strain, which also produced an extended-spectrum β-lactamase encoded by the blaCTX-M-15 gene, carried on a plasmid that is a member of a very rarely reported family of phage-like plasmids. This is the first time an in-depth sequence analysis has been done on a blaCTX-M-15- containing phage-like plasmid, the presence of which suggests a new emerging mechanism of AR gene transmission.
Keywords: ST131; phage-like plasmid; surface water.