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Background  Chromosomally encoded AmpC β-lactamases may be acquired by transmissible plasmids which consequently can disseminate into bacteria lacking or poorly expressing a chromosomal  bla  AmpC  gene. Nowadays, these plasmid-mediated AmpC β-lactamases are found in different bacterial species, namely  Enterobacteriaceae , which typically do not express these types of β-lactamase such as  Klebsiella  spp. or  Escherichia coli . This study was performed to characterize two  E. coli  isolates collected in two different Portuguese hospitals, both carrying a novel CMY-2-type β-lactamase-encoding gene.    Findings  Both isolates, INSRA1169 and INSRA3413, and their respective transformants, were non-susceptible to amoxicillin, amoxicillin plus clavulanic acid, cephalothin, cefoxitin, ceftazidime and cefotaxime, but susceptible to cefepime and imipenem, and presented evidence of synergy between cloxacilin and cefoxitin and/or ceftazidime. The genetic characterization of both isolates revealed the presence of  bla  CMY-46  and  bla  CMY-50  genes, respectively, and the following three resistance-encoding regions: a  Citrobacter freundii  chromosome-type structure encompassing a  blc-sugE-bla  CMY-2-type  -ampR  platform; a  sul 1-type class 1 integron with two antibiotic resistance gene cassettes ( dfrA1  and  aadA1 ); and a truncated mercury resistance operon.    Conclusions  This study describes two new  bla  CMY-2-type  genes in  E. coli  isolates, located within a  C. freundii -derived fragment, which may suggest their mobilization through mobile genetic elements. The presence of the three different resistance regions in these isolates, with diverse genetic determinants of resistance and mobile elements, may further contribute to the emergence and spread of these genes, both at a chromosomal or/and plasmid level.

Two novel CMY-2-type β-lactamases encountered in clinical Escherichia coli isolates