Phenotypic Carbapenemase Production and blaOXA detecting by PCR in Acinetobacter baumannii isolates from a Hospital of Infectious Diseases from North-East Romania

Introduction: In the last 40 years, Acinetobacter baumannii has been among the bacteria known to acquire multiple mechanisms of antibiotic resistance and, as a result, it is now one of the pathogens involved in healthcare-associated infections with multidrug resistant strains. Our study aimed to assess the production of carbapenemases in carbapenem-resistant A. baumannii by means of phenotypic methods and polymerase chain reaction technique (PCR), as well as to appraise the performances of carbapenemase detection by phenotypic tests compared to the PCR approach.

Materials and Methods: We used phenotypic methods (E-test MBL, CIM, MHT, Rosco® Kit/OXA/MBL, OXA-23 K-SeT® assay) to investigate the production of carbapenemases in 43 carbapenem-resistant A. baumannii isolates, and PCR to screen for the genes bla_OXA-23, bla_OXA-24, bla_OXA-58, bla_OXA-51, bla_VIM, bla_IMP and bla_NDM.

Results: The carbapenem inactivation method (CIM) at 2 hours, CIM at 4h, OXA-23 K-SeT® assay, Rosco® Kit/OXA, and modified Hodge test (MHT) identified 26%, 63%, 65%, 81%, and 42% carbapenemase-producing isolates, respectively. The phenotypic E-test MBL detected metallo-β-lactamase (MBL) production in 79% of strains. PCR revealed blaOXA-51 in all the isolates, bla_OXA-23 in 35/43 (81%), bla_OXA-24 in 28/43 (65%), bla_VIM in 7/43 (3%) and bla_OXA-58, bla_IMP, bla_NDM were not detected.

Conclusion: Because phenotypic tests do not highlight all the carbapenemase-producing strains, their results must be interpreted with caution relative to their level of performance, and negative results should be confirmed by means of PCR.