Spread of Gram-negative bacteria producing extended-spectrum beta-lactamases (ESBLs) and carbapenemases constitutes a growing challenge in control of bacterial infections. In this study, prevalence and genetic characteristics of Escherichia coli and Klebsiella pneumoniae harboring ESBL and/or carbapenemase genes, with other beta-lactamase/resistance genes, were investigated for a total of 375 clinical isolates in Mymensingh located in north-central Bangladesh. The major ESBL gene was bla_CTX-M-1 group, which was detected in 33.9% and 51.4% of E. coli and K. pneumoniae, respectively, with CTX-M-15 gene being dominant. SHV-type beta-lactamase genes, including newly identified alleles (SHV-201 and SHV-202) were detected at higher rate in K. pneumoniae (27%). Nine isolates of E. coli (3.9%) harbored carbapenemase genes; bla_NDM-1 (phylogenetic group A-sequence type 2104 (A-ST2104), B2-ST73), bla_NDM-5 (A-ST167, B2-ST38/ST2659-related STs), and bla_NDM-7 (B1-ST101/ST224, D-ST6682). AmpC beta-lactamase genes (bla_CMY-2 and bla_CMY-42) were detected in E. coli, which mostly harbored bla_CTX-M-15 and plasmid-mediated quinolone resistance (PMQR) determinants (aac6'-Ib-cr, qnrB, qnrS, qepA, and oqxAB). A new CMY allele (CMY-160) belonging to CMY-2 group was identified in phylogenetic group D E. coli. Among K. pneumoniae, carbapenemase gene was detected in three isolates (2%); bla_NDM-1 in ST11 and ST1322, and bla_OXA-181 in ST43 isolate. As well as higher rate of aac6'-Ib-cr in K. pneumoniae (39%), PMQR gene oqxAB was also commonly found among isolates analyzed. These findings indicated spread of bla_NDM genes to diverse E. coli clones and emergence of bla_OXA-181 in K. pneumoniae, with increased prevalence of ESBLs represented by CTX-M-15 in Bangladesh.

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