Surveillance of bacterial resistance and study on β-lactamases in cefoxitin-resistant Klebsiella pneumoniae isolates

Objective To investigate the resistance and β-lactamase of cefoxitin-resistant Klebsiella pneumoniae. Methods The minimal inhibitory concentrations were determined by standard agar dilution.Isoelectric focusing was used to measure the PI(s) of an isolate,s β-lactamase,AmpC and ESBLs activity was confirmed by a three-dimensional extract method. Results The resistant rates of 40 strains were as follows: imipenem and meropenem 0.0%,cefepime 20.6%,cefotaxime(22.5%),ceftazidime 60.0%.The most isolates were demonstrated two or more β-lactamase bands by IEF.Of 39 strains tested,ESBLs was detected in 31(70.5%) strains and AmpC-typeβ-lactamase in 16(41.0%) strains by three dimensional extract test. Conclusions These cefoxitin-resistant Klebsiella pneumoniae produced two or more β-lactamases.It is imperative for clinical microbiology laboratories to detect and research β-lactamases,especially AmpC enzyme.