Occurrence and Detection of AmpC β-lactmases and plasmid-mediated ampC among Escherichia coli

Objective To detect AmpC-producing β-lactmase,and plasmid-mediated ampC genes in clinical isolates of Escherichia coli(E.coli).Methods Forty E.coli isolates phenotypically characterized as putative AmpC β-lactmase producers were collected.MICs were determined by the NCCLS broth microdilution(BMD) method.AmpC and ESBLs β-lactmase were detected by three-dimensional extract test(TDET).The presence of plasmid-mediated ampC and ESBLs genes were determined by PCR and conjugal transfer assays of the ampC resistance determinants were carried out by broth mating procedure.Results Of the 40 E.coli,39 showed β-lactamase activity in TDET,21 were positive for both ESBLs and AmpC β-lactamases,15 for ESBLs,and 3 for AmpC.In the 8 of 40 isolates,2 kinds of ampC specific amplication products were observed,of which 7 were CIT type,and 1 was DHA type.PCR showed that the thirty-four isolates contained at least one of the genes blaTEM,blaOXA,blaCTX-M,but no blaSHV.Nine transconjugants were selected from 8 donor isolates producing plasmid-mediated AmpC β-lactamase.Conclusions Present findings indicate that AmpC-producing E.coli are present in this hospital,and AmpC-encoding plasmids are transferable.