Carbapenemases and efflux pumps in clinical Acinetobacter baumannii: biomolecular characterization of multi-drug resistant isolates from a hospital in Central Italy

Abstract

Purpose: Multi-drug resistant (MDR) Acinetobacter baumannii is increasingly responsible of hospital-acquired infections, mainly in intensive care units (ICUs). Aims of this study were to assess antibiotic resistance phenotypes and clonal relationships in A. baumannii isolates from hospital setting, and to evaluate circulating carbapenemases (blaKPC, blaGES, blaSHV, blaIMP, blaVIM, blaNDM, blaGIM, blaAmpC, blaOXA-23, blaOXA-24, blaOXA-51, blaOXA-58). Prevalence of multi-drug efflux pumps encoding genes (adeB, adeG, adeJ, abeS, craA, abeM) and their negative regulator (soxR) was also determined. Methods & Materials: Clinical A.baumannii (n = 24) were collected from “A.Cardarelli” hospital (95.8% from ICU), in Molise Region (Central Italy). The Minimum Inhibitory Concentration (MIC) was assessed for 20 antibiotics by BD Phoenix™, including carbapenems (imipenem and meropenem). Molecular typing was performed through Pulsed-Field Gel Electrophoresis (PFGE) with ApaI and AscI enzymes, while PCR assays were carried out to detect carbapenemases and multi-drug efflux pumps encoding genes. Results: A.baumannii strains were resistant to almost all antibiotics, including carbapenems. The combined ApaI/AscI dendrogram analysis revealed four clusters and seven pulsotypes at 95% similarity (Simpson Index: D = 84.0%). Among resistance genes, all strains harboured blaOXA-23, blaOXA-51 and blaAmpC, and 33.3% (n = 8) blaVIM, while blaKPC, blaGES, blaSHV, blaIMP, blaNDM, blaGIM, blaOXA-24, and blaOXA-58 were never detected. On multi-drug resistance mediated by efflux pumps, all isolates were adeB, adeG, adeJ, soxR and abeS positive, while abeM and craA were not found. Conclusion: The study findings highlight the circulation of MDR A.baumannii in hospital ICU, underlining the urgent need of strategies for limiting their spread. Molecular epidemiology showed that isolates are characterized by a remarkable resistance to carbapenems, explained by the highest prevalence of blaOXA-23 and blaOXA-51, in line with other Italian studies. Interestingly, detection of blaVIM suggest an important increase of this carbapenemase circulation, which is occasionally found in A.baumannii in Italy. The lack of other resistance genes confirm their very low occurrence, according to nationwide distribution. The value of D confirms the need of integrate other typing methods with PFGE. Further studies are required to evaluate clonal diversity through Sequence Types distribution and on the efflux pumps role in resistance mechanisms by transcriptional level analysis.