High prevalence of blaCMY AmpC beta-lactamase in ESBL co-producing Escherichia coli and Klebsiella spp. clinical isolates in the northeast of Iran

•A total of 55.8% of E. coli and Klebsiella spp. isolates were identified as putative ESBL-producers.•A total16.7% of ESBL producing E. coli and Klebsiella spp. were positive for plasmid-borne AmpC genes.•blaCMY-type was the most frequent genotype of pAmpC among ESBL producing E. coli and Klebsiella spp. The production of β-lactamase enzymes such as AmpC β-lactamases and extended-spectrum β-lactamases (ESBLs) is among the main mechanisms for resistance to expanded-spectrum cephalosporins. The present study was conducted to investigate the prevalence and molecular epidemiology of plasmid-mediated AmpC beta (β)-lactamase in ESBL co-producing Escherichia coli (E. coli) and Klebsiella spp. (Klebsiella pneumoniae and Klebsiella oxytoca) clinical isolates in the northeast of Iran. A total of 602 E. coli and Klebsiella spp. clinical isolates were collected from three hospitals in Mashhad (northeast of Iran). A combination disk test (CDT) was performed for the phenotypic detection of ESBLs. Screening for the detection of AmpC β-lactamases was performed by a susceptibility test to a cefoxitin disc among ESBL producing isolates. A confirmatory test for AmpC β-lactamases was performed using the Mast® D68C test. Identification of plasmid-mediated AmpC cluster genes was done by multiplex polymerase chain reaction (PCR). Among 336 ESBL-producing strains, 230 (68.4%) isolates were resistant to cefoxitin. Results of the Mast® D68C test showed that 30% (69/230) of cefoxitin-resistant isolates simultaneously exhibited ESBL and AmpC activity and 22% (51/230) of isolates probably showed multi-drug resistant (MDR) phenotype. Results of multiplex PCR among ESBL-positive isolates showed that, 16.7% (56/336) of isolates were positive for plasmid-borneampC cluster genes, and CMY (38%) was the most frequent genotype of plasmid mediated AmpC. Findings of the study revealed that an increase in the prevalence of ESBL and AmpC co-producer in E. coli and Klebsiella spp. strains may become an important public health issue. Therefore, there is a vital need for surveillance of spread of these clinical isolates.