Reduced antibiotics sensitivity of Acinetobaoter baumannii induced by meropenem in vitro and related mechanism / 中华临床感染病杂志

ABSTRACT

Objective To investigate the mechanism related to reduced antibiotic sensitivity of Acinetobacter baumannii inducted by meropenem in vitro.Methods Three strains of clinically isolated carbapenems-sensitive Acinetobacter baumannii were induced by meropenem in vitro, and the mutant strains (MS1, MS2 and MS3) were obtained.Minimal inhibitory concentrations (MICs) of antimicrobial agents to strains before and after induction were determined by automatic drug sensitivity analyzer .The homology of strains was analyzed by Enterobacterial repetitive intergenic consensus -polymerase chain reaction ( ERIC-PCR).Modified Hodge test and EDTA-Na2-double disk synergy test were used to detect carbapenemase and metallo-β-lactamase (MBL), respectively.Main carbapenemase genes were detected by PCR and followed by DNA sequencing.Expressions of adeB and outer membrane proteins in strains before and after induction were detected with fluorescence quantitative PCR and SDS -polyacrylamide gel electrophoresis , respectively.t test was used for data analysis .Results The sensitivity of mutant Acinetobacter baumannii strains to meropenem and most antibiotics was reduced , except to imipenem, amikacin and polymyxin; and the reduced sensitivity to meropenem in MS2 and MS3 was of genetic stability.ERIC-PCR showed 100%homology between the mutant strains and parental strains .Both carbapenemase and metallo -β-lactamase were negative in mutant strains and parental strains , and only OXA-51 gene was found.The expressions of adeB gene in mutant strains were 24.26 ±0.91, while those in parental strains were 22.81 ±0.38, and the difference was not significant (t =2.534, P >0.05).Outer membrane protein with molecular weight 54 000 was missing in MS1, while that with molecular weight 47 000 was missing in MS2 and MS3.Conclusion Reduced antibiotics sensitivity in meropenem -induced Acinetobacter baumannii may be correlated with the deficiency of outer membrane protein with molecular weight 47 000.