Insertion Sequences within Oxacillinases Genes as Molecular Determinants of Acinetobacter baumannii Resistance to Carbapenems—A Pilot Study

Carbapenem-resistant <i>Acinetobacter baumannii</i> is one of the major problems among hospitalized patients. The presence of multiple virulence factors results in bacteria persistence in the hospital environment. It facilitates bacterial transmission between patients, causing various types of infections, mostly ventilator-associated pneumonia and wound and bloodstream infections. <i>A. baumannii</i> has a variable number of resistance mechanisms, but the most commonly produced are carbapenem-hydrolyzing class D β-lactamases (CHDLs). In our study, the presence of <i>bla</i>_OXA-23, <i>bla</i>_OXA-40 and <i>bla</i>_OXA-51 genes was investigated among 88 clinical isolates of <i>A. baumannii</i>, including 53 (60.2%) strains resistant to both carbapenems (meropenem and imipenem) and 35 (39.8%) strains susceptible to at least meropenem. Among these bacteria, all the isolates carried the <i>bla</i>_OXA-51 gene. The <i>bla</i>_OXA-23 and <i>bla</i>_OXA-40 genes were detected in two (5.7%) and three (8.6%) strains, respectively. Among the OXA-23 carbapenemase-producing <i>A. baumannii</i> strains (<i>n</i> = 55), insertion sequences (IS<i>Aba1</i>) were detected upstream of the <i>bla</i>_OXA-23 gene in fifty-two (94.5%) carbapenem-resistant and two (3.6%) meropenem-susceptible isolates. <i>A. baumannii</i> clinical strains from Poland have a similar antimicrobial resistance profile as those worldwide, with the presence of IS<i>Aba1</i> among <i>bla</i>_OXA-23-positive isolates also being quite common. Carbapenem resistance among <i>A. baumannii</i> strains is associated with the presence of CHDLs, especially when insertion sequences are present.