Distribution of plasmid-mediated AmpC β-lactamase in Escherichia coli and Klebsiella spp

Objective To investigate the phenotype,genotype and distribution of plasmid-mediated AmpC β-lactamases in Escherichia coli and Klebsiella spp. Methods 1 935 Escherichia coli and Klebsiella spp were detected by standard disc diffusion method as screen test for AmpC lactamase.Three-dimensional extract test,multiplex polymerase chain reaction(PCR),isoelectric focusing analysis(IEF),conjugation,PCR and sequencing were performed on positive strains to determine the phenotype and genotype of AmpC β-lactamases. Results 327,85,54 strains were positive by standard disc diffusion,three-dimensional extract test and multiplex PCR respectively.4 of 13 strains could transfer cefoxition resistance to the recipient.IEF proved that they produced a β-lactamase whose isoelectric point(pI) was 9.0 and could be inhibited by cloxacillin and not by clavulnate. Conclusions 54 of 1 935(2.79%) clinical isolates of our hospital harboured plasmid-mediated AmpC β-lactamases including DHA like and CIT like ampC genes.