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Objective: Acinetobacter baumannii has become an important problem because of the high drug resistance rate. The aim of this study was to assess the antimicrobial resistance profile and explore the role of membrane porin in imipenem resistance of A baumannii., Methods: A total of 63 isolates of imipenem-resistant A baumannii (IRAB) and 21 of imipenem-sensitive A baumannii (ISAB) were collected. Susceptibility testing to 16 kinds of antimicrobial agents was conducted by K-B method. PCR technique was used to detect carO and oprD genes, and sequencing was performed to compare the sequence between IRAB and ISAB. Three-dimensional structure model of CarO protein was established., Results: While ISAB isolates presented sensitive to most classes of antibiotics, isolates of IRAB displayed much higher resistance rate except tigecycline (3.2%), cefoperazone/sulbactam (28.6%), and minocycline (30.2%). All 84 isolates were observed carrying both carO and oprD genes. Further sequencing revealed important mutations of carO gene existed in IRAB in comparison with ISAB. Meanwhile, significant differences in three-dimensional structure of carO protein molecule were also found between IRAB and ISAB., Conclusions: The drug resistance profile of IRAB is increasingly severe in clinical settings. Mutation of CarO was identified as one of the molecular mechanisms involved in imipenem resistance in A baumannii., (© 2019 The Authors. Journal of Clinical Laboratory Analysis Published by Wiley Periodicals, Inc.)

Background: To investigate the role of efflux pumps AdeABC, AdeIJK, AdeDE and AbeM in reduced susceptibility to imipenem in clinical isolates of Acinetobacter baumannii., Methods: Susceptibility testing was conducted by the agar dilution method. The presence and expression of pump genes were analyzed by conventional PCR and real-time RT-PCR, respectively., Results: Most antibiotics, including carbapenem, aminoglycosides, fluoroquinolones and cephalosporins showed high minimum inhibitory concentration (MIC) values in imipenem-resistant A. baumannii (IRAB). After exposure to the efflux pump inhibitor Phe-Arg-β-naphthylamide, a 4- to 32-fold reduction of imipenem MICs was observed in 33 (66%) isolates of IRAB, while no significant decrease occurred in imipenem-susceptible A. baumannii (ISAB). The majority of IRAB isolates (>80%) were found to be positive for adeB, adeR, adeS, adeJ and abeM. Positive adeE was discovered in 6 isolates of IRAB and coexisted with adeB. Approximate 4-, 3- and 11-fold increases in adeB, adeJ and abeM expression were observed, respectively, in IRAB compared to those in ISAB., Conclusions: A variety of efflux pump systems, including AdeABC, AdeIJK and AbeM, seem to play important roles in the resistance to imipenem of A. baumannii. Moreover, this is the first time that adeE has been found to coexist with adeB in a small number of isolates of A. baumannii., (Copyright © 2012 S. Karger AG, Basel.)