A study on mechanism for resistance of carbapenems in Acinetobacter baumannii

Objective To investigate the mechanism of Acinetobacter baumannii resistant to carbapenems.Methods E test and microdilution were used to determine the minimum inhibitory concentrations(MIC) of 11 antibiotics against 30 isolates of imipenem-resistant Acinetobacter baumannii strains.The production of β-lactamase was detected by improved three-dimensional test.Nine coding genes ofβ-lactamase were detected by PCR.Results The resistance rates of 11 antibiotics were over 90% except for polymyxin B(23.3%) and ciprofloxacin(87.7%).Among 30 isolates of Acinetobacter baumannii the positive rate of single ESBLs,single AmpC,ESBLs+AmpC,non-ESBLs non AmpCβ-lactamase was 33.3%(10/30),3.3%(1/30),23.3%(7/30) and 26.7%(8/30) respectively by three-dimensional test.The coding genes:VIM-1,VIM-2,OXA-24,CTX-M-2,IMP-1 and VEB-1 were undetectable.Two or three of coding genes:OXA-23,PER-1 and AmpC were detectable in 27 isolates,and their homologies compared with corresponding sequences of GenBank were more than 98%.A nucleotide mutation(A→C) at 617 site of PER-1 gene was found in No.26 strain,so this sequence was registered in GenBank(Accession No.DQ341275).Conclusions Carbapenems resistance in Acinetobacter baumannii related with the production of OXA-23,PER-1 and AmpC.