Study on β-lactams resistance and genotype of β-lactamases in plasmid-mediated AmpC β-lactamases and ESBLs producing bacteria

Objective To investigate the β-lactams resistance and genotype characteristics of β-lactamases in plasmid-mediated AmpC β-lactamases and extended-spectrum β-lactamases (ESBLs) producing K.pneumoniae and E.coli . Methods A total of 110 clinical isolates of nonrepetitive drug-resistant K.pneumoniae and E.coli were detected by three-dimensional extract test for AmpC β-lactamases and phenotypic confirmatory test based on the National Committee for Clinical Laboratory Standard (NCCLS) criteria for ESBLs. The minimal inhibitory concentrations (MICs) on AmpC β-lactamases and ESBLs producing strains and the isoelectric points(pIs) of β-lactamases were determined by standard agar dilution and isoelectric focusing(IEF). Drug resistant gene were positioned by plasmids conjugation experiments. Universal primer PCR for AmpC and ESBLs gene amplification and DNA sequencing were carried out for genotype of β-lactamases. Results The incident rate of AmpC β-lactamases and ESBLs producing strains were 7.7%(5/65) in K.pneumoniae and 8.9%(4/45) in E.coli. The sensitivity to third-generation cephalosporins,aztreonam,cefmetazole and antibiotics combined with inhibitors for AmpC β-lactamases and ESBLs producing strains was very low,but all sensitive to imipenem. IEF demonstrated that 9 isolates displayed 2-3 bands of β-lactamases activity with pI 5.4-9.0. AmpC β-lactamases were DHA-1 type in 9 strains,ACT-1 was also identified in 1. ESBLs were CTX-M type with CTX-M-14,CTX-M-3 and CTX-M-9 in 4,3,2 strains respectively. Furthermore,3 of them were also found to carry broad-spectrum β- lactamases TEM-1 gene. Conclusion There are epidemic strains of K.pneumoniae and E.coli producing plasmid-mediated DHA-1,ACT-1 type AmpC β-lactamases and CTX-M type ESBLs in our hospital,sensitivity test shows that they are resistant to the most new broad-spectrum β-lactamas but sensitive to imipenem.