ABSTRACT: Objectives:To describe the molecular characteristics of beta-lactamases in bloodstream-infection Escherichia coli isolated from elderly patients, and to determine the genotypic patterns of bla CMY - 2 and bla ADC - 162. Methods:A total of 50 bloodstream-infection E. coli isolates were obtained from patients aged > 50 years at Shanghai Sixth People's Hospital South Campus during 2015-2018. The isolates were subjected to beta-lactamase detection using phenotypic and molecular methods. Beta-lactamase genes were verified by sequencing and the phylogenetic relationships of the isolates were analyzed by multilocus sequence typing (MLST). The transferability of plasmids carrying bla CMY- 2 and bla ADC- 162 genes was verified by conjugation experiments and plasmid replicon typing. Results:Eight beta-lactamase subtypes were detected in 50 isolates of bloodstream-infection E. coli. bla TEM- 1 (21/50) was the most common beta-lactamase gene, followed by bla CTX-M- 14 (8/50), bla OXA- 27 (5/50), bla CTX-M- 27 (3/50), bla CTX-M- 65 (1/50), bla ADC- 162 (1/50), and bla CMY- 2 (1/50). Of these, bla ADC- 162 (ST95-A), and bla CMY- 2 (ST95-B2) have not previously been reported in bloodstream-infection E. coli. In 21 isolates, beta-lactamase genes were located on conjugative plasmids belonging to incompatibility groups FrepB (n = 7), FIA (n = 1), FIC (n = 2), K (n = 8), N (n = 1), and I (n = 1), and bla CTX-M was associated with the common elements ISEcp1, IS903, and IS26, but with special sequences (region V, region Y, and region W) for ISEcp1 in 14 isolates. Conclusion:To the best of our knowledge, this study provides the first molecular characterization of beta-lactamase genes in E. coli isolated from the bloodstream in elderly patients. Beta-lactamase genes were detected at a relatively high frequency in elderly patients with bloodstream E. coli infections. Plasmid replicon analysis showed that horizontal dissemination of beta-lactamase genes was mainly mediated by IncK and IncF plasmids, which could encode multidrug resistance genes. The study also provides the first report of ISAba1-bla ADC - 162-tnpA and ISEcp1-bla CTX-M- 14-IS903-bla CMY- 2-blc-sugE in E. coli, and demonstrates IncF plasmid-mediated bla ADC - 162 and bla CMY- 2 gene dissemination among bacteria.
