CHARACTERIZATION OF PLASMIDS HARBORING blaOXA-58 IN CLONALLY RELATED MULTIRESISTANT Acinetobacter baumannii CLINICAL STRAINS

MORAN BARRIO J; CAMERANESI MM; LIMANSKY AS; VIALE AM

Congreso; X Congreso de Microbiología General - SAMIGE 2014; 2014

Sociedad Argentina de Microbiología (SAMIGE)

Acinetobacter baumannii is an important opportunistic pathogen responsible for a variety of nosocomial infections and outbreaks that can rapidly evolve multidrug resistance (MDR) when confronted with antibiotic therapy. In this context, the acquisition of resistance determinants mediated by horizontal gene transfer (HGT) is considered a major determinant of MDR particularly in environments under strong antibiotic pressure such as the clinical setting. In particular, the emerging resistance to carbapenems represents a major concern worldwide. One of the mechanisms playing a significant role in A. baumannii carbapenem resistance is the production of OXA-type carbapenemases, whose genes are generally carried by plasmids. Thus, the analysis and understanding of the dissemination mechanisms of genetic platforms carrying the blaOXA-58 genes is fundamental for the prevention of outbreaks. In this context, we have recently described the presence of a plasmid overexpressing blaOXA-58 as a result of an ISAba825-generated hybrid promoter which largely enhances the carbapenem resistance to harboring bacteria. We additionally found that this arrangement can be carried in an adaptability module. Here we present the characterization of two different plasmids (pAb242 and pAb825), both carrying the ISAba825-blaOXA-58 arrangement, which were isolated from clonally related carbapenem-resistant clinical A. baumannii strains designated Ab242 and Ab825, respectively. Both plasmids were isolated from the corresponding strains, used to transform the A. baumannii ATCC 17978 multisensitive strain, and further selecting for imipenem (IPM) resistance. We found that both plasmids could replicate and could direct expression of blaOXA-58 gene in this new host, as shown by the 8-fold increases in MIC values towards IPM (from 0.5 mg/ml to 4 mg/ml for both ATCC 17978 transformants). Production of OXA-58 was evident as judged by SDS-PAGE analysis of bacterial extracts. Restriction analysis of pAb242 and pAb825 recovered from recombinant bacteria showed however relevant differences in sizes indicating that both plasmids are similar but not identical. Overall, the presence of ISAba825-blaOXA-58 in plasmids from clonally related A. baumannii clinical strains suggest dissemination of this arrangement through HGT and further selection by carbapenem pressure in the nosocomial environment. The possibility of transference of the adaptability module between A. baumannii plasmids is discussed.