Detection of antibiotic resistance conferred by extended-spectrum beta-lactamases and AmpC beta-lactamases in gram-negative bacilli

ObjectiveTo investigate the antibiotic resistance conferred by extended-spectrum β-lactamases(ESBLs) and AmpC β-lactamases in gram-negative bacilli isolated in Tongling.MethodsAntimicrobial susceptibility testing was done on 270 strains of gram negative bacilli isolated in Tongling from October 2003 to September 2004 by Kirby-Bauer method.Results were interpreted according to NCCLS 2002 standards.ESBLs and AmpC β-lactamases was detected by three-dimensional test.Results(Among) 270 gram negative bacilli,68 strains(25.2%) were ESBLs and/or AmpC β-lactamases hyperproducer.Of the 68 strains,49 were only ESBLs hyperproducer,most prevalent in K.pneumoniae(31.6%) and E.coli(31.0%).All the 3 only AmpC β-lactamases hyperproducer were E.cloacae.Additionally,16 strains were hyperproducer of both ESBLs and AmpC β-lactamases,mainly A.baumannii(n=8).The resistance of ESBLs and AmpC β-lactamases producing strains to most antimicrobials were much higher than those without producing ESBLs or AmpC β-lactamases.Resistance rates of ESBLs-producing strains against ticarcillin-clavulanic acid and cefoperazone-tazobactam were higher than 50%,but more susceptible to imipenem.ConclusionsESBLs and AmpC β-lactamases are two main enzyme types conferring resistance to β-lactam antibiotics in clinical isolates of gram negative bacilli.Imipenem could be the first choice for treating infections caused by gram negative bacilli producing ESBLs or AmpC β-lactamases.