Study on antimicrobial resistance and detection of AmpC and extended-spectrum β-lactamases-producing strains in a respiratory intensive care unit

Objective To investigate antimicrobial resistance and the prevalence of AmpC β-lactamases and extended-spectrum β-lactamases(ESBLs)-producing gram-negative bacteria from specimens of a respiratory intensive care unit(RICU).Methods AmpC β-lactamases-producing and AmpC β-lactamases combined with ESBLs-producing strains were detected by three-dimensional test,ESBLs-producing isolates were identified with the method recommended by the National Committee for Clinical Laboratory Standard(NCCLS).Antimicrobial susceptibility of AmpC β-lactamases and ESBLs-producing strains were detected by Kirby-Bauer and E-test methods.Results AmpC β-lactamases,ESBLs and AmpC β-lactamases combined with ESBLs-producing strains were found in 28(16.67%),71(42.26%)and 12(7.14%)strains respectively.The most common AmpC β-lactamases-producing strains was Enterobacter cloacae(57.14%);Among ESBLs-producing strains,the most common isolates were Klebsiella pneumoniae(71.70%)and Escherichia coli(55.81%).The AmpC β-lactamases-producing strains were more susceptible to imipenem and cefepime,the resistant rate of which was 3.57% and 28.57% respectively.The resistant rate of ESBLs-producing strains to imipenem,piperacillin/tazobactam and cefoperazone/sulbactam was 2.82%,32.39% and 25.35% respectively.AmpC β-lactamases combined with ESBLs-producing strains were only sensitive to imipenem,imipenem-resistant strain was not found.Conclusion AmpC β-lactamases and ESBLs-producing gram-negative strains are common in clinical isolates from RICU,and resistance to the majority of new broad-spectrum β-lactamas,but sensitive to imipenem.