Detection of AmpC β-lactamases in Cefoxitin-resistant Klebsiella pneumonia and Analysis on Its Antimicrobial Resistance Genes

Objective To detect AmpC β-lactamases and extended-spectrum β-lactamases(ESBLs)in cefoxitin-resistant Klebsiella pneumonia,and to investigate the effects of AmpC genes on drug-resistant phenotype.Methods Three-dimensional extract test was used to detect AmpC β-lactamases,and ESBLs were detected by double-disk confirming test.PCR for AmpC and ESBLs gene amplification and DNA sequencing were carried out for identifying the genotypes of β-lactamases.Results Among 72 strains of cefoxitin-resistant Klebsiella pneumonia,45 AmpC-producing strains were detected,with the positive rate of 62.5%(45/72).There were 2 strains with CMY-2 group and 43 strains with DHA-1 group detected in 45 strains of Klebsiella pneumonia,CMY-2 and DHA-1 were simultaneously carried in one strain.33 of 45 AmpC-positive Klebsiella pneumoniae strains were ESBLs-producing strains,with the detection rate of 73.3%(33/45).There were 23 strains carrying bla(CTX-M)gene,15 strains carrying bla(SHV)gene,and 19 strains carrying bla(TEM)gene detected in 33 ESBLs-positive strains which expressed multiple drug resistance gene carrying.Conclusions The detection rate of ESBLs in AmpC-positive Klebsiella pneumoniae is high,and therefore the surveillance of over-expressing AmpC β-lactamase in cefoxitin-resistant positive Klebsiella pneumonia must be enhanced.Imipenem and meropenem should be used as primary therapy for the infections caused by the related bacillus.The drug resistant rates of AmpC-and ESBLs-producing Klebsiella pneumonia to imipenem and meropenem are both lower than those of AmpC-producing Klebsiella pneumonia.