Abstract: Objective To investigate β-lactamase gene and class 1 integron gene of 60 clinical Acinetobacter baumannii isolates. Methods The minimal inhibitory concentrations (MICs）for 16 antibiotics widely used in clinic were determined using the standard broth microdilution method. The β-lactamase gene, class 1 integron gene and adeB gene were determined by PCR and were then sequenced. Results Fifty-three strains of the 60 A. baumanii isolates were multi-drug resistant. OXA-23 gene was detected positive in six A. baumanii isolates, which were all resistant to more than five antimicrobial agents including carbapenem and showed high resistance to many antibiotics. The 38 strains that carried PER-1 gene showed higher resistance to cephalosporins than those without this gene (P<0.01). Class 1 integron gene was positive in 45 strains, which exhibited significantly higher multiple resistance than those without this gene (P<0.01). The 25 strains carrying both class 1 integron and PER-1 genes had a markedly higher multiple resistance (P<0.01), but not in resistant level, compared to the 7 strains without these two genes. Conclusion Class 1 integron and β-lactamase gene may be the causes of multidrug-resistance of A. baumanii. The strains carrying OXA-23 gene always showed multiple and high resistance to several antibiotics, so effective measures must be taken to control the epidemic of these strains.

Key words: Acinetobacter baumannii, Multidrug-resistance, molecular mechanism