Characteristics of multidrug-resistant Acinetobacter baumannii strains isolated in Geneva during colonization or infection

This study determined the antibiotic susceptibility profile and genetic mechanisms of β-lactam resistance in 27 clinical strains of Acinetobacter baumannii isolated at the University Hospitals of Geneva, Switzerland. The antimicrobial susceptibility testing was performed using Etest and the disc diffusion method in accordance with CLSI guidelines. All of the strains were defined as multi-drug resistant (MDR) and were susceptible to colistin and moderately susceptible to tigecycline. Uniplex PCR assays were used to detect the following β-lactamase genes: four class D carbapenem-hydrolysing oxacillinases (blaOXA-51, blaOXA-23, blaOXA-24 and blaOXA-58), four class B metallo-β-lactamases genes (blaIMP, blaVIM, blaSPM and blaNDM) and two class A carbapenemases (blaKPC and blaGES). All of the strains were positive for blaOXA-51 (intrinsic resistance), 14/27 strains carried blaOXA-23, 2/27 strains carried a blaOXA-24-like gene, and 4/27 strains had a blaOXA-58 gene. blaGES-11 was found in three strains, and NDM-1-harbouring strains were identified in three patients. All of the A. baumannii isolates were typed by rep-PCR (DiversiLab) and excluded any clonality. Altogether, this analysis suggests a very high genetic diversity of imported MDR A. baumannii.