Antibiotic resistance determinants of Acinetobacter baumannii strains isolated from nosocomial infections

Over the years, intensive use or the misuse of antibiotics triggered the selection of multidrug resistant bacteria making it harder to treat common infectious diseases. Some of the most dangerous microbial threats are commonly united under the acronym "ESKAPE" (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species). Among these, A. baumannii has acquired resistance to a vast array of antimicrobials in recent decades. This capacity is partly dependent on the ability of this bacterium to acquire resistance genes, often by horizontal gene transfer. In our study, a total of 25 clinical strains of A. bumannii were isolated during 2015-2016 from patients hospitalized at the National Institute for Cardiovascular Diseases Prof. C.C. Iliescu. The selected strains were isolated from nasal (n = 11) and tracheal secretions (n=14). Strain identification and antibiotic susceptibility testing were performed using Vitek2 system in the Microbiology laboratory of the National Institute for Cardiovascular Diseases Prof. C.C. Iliescu. Molecular analysis of beta-lactam resistance genes revealed the presence of the genes encoding class D beta-lactamases such as bla(OXA-51) (32% of the investigated strains), bla(OXA-23) (24%), bla(OXA)(-24) (8%) and metallo-beta-lactamases encoded by bla(VIM)(-2 )gene(16% of the strains), the most frequently encountered ones, followed by the less encountered bla(IMP) (12%) and bla(OX)(A-24) (8%) genes. One strain of A. baumannii exhibited resistance to tetracycline encoded by letA (4%) and one to quinolones determined by the presence of the qnrS gene (4%). On the other hand, qnrA, qnrB and tetB were not found among A. baumannii isolates. We show here that 50% of analysed strains were isolated from tracheal secretion and nasal exudates and 16% of A. bumannii strains exhibited the Multidrug Resistance phenotype (MDR).