Analysis of bla(CHDL) Genes and Insertion Sequences Related to Carbapenem Resistance in Acinetobacter baumannii Clinical Strains Isolated in Warsaw, Poland

Acinetobacter baumannii is an important cause of nosocomial infections worldwide. The elucidation of the carbapenem resistance mechanisms of hospital strains is necessary for the effective treatment and prevention of resistance gene transmission. The main mechanism of carbapenem resistance in A. baumannii is carbapenemases, whose expressions are affected by the presence of insertion sequences (ISs) upstream of bla(CHDL) genes. In this study, 61 imipenem-nonsusceptible A. baumannii isolates were characterized using phenotypic (drug-susceptibility profile using CarbaAcineto NP) and molecular methods. Pulsed field gel electrophoresis (PFGE) and multi-locus sequence typing (MLST) methods were utilized for the genotyping. The majority of isolates (59/61) carried one of the following acquired bla(CHDL) genes: bla(OXA-24-like) (39/59), ISAba1-bla(OXA-23-like) (14/59) or ISAba3-bla(OXA-58-like) (6/59). Whole genome sequence analysis of 15 selected isolates identified the following intrinsic bla(OXA-66) (OXA-51-like; n = 15) and acquired class D β-lactamases (CHDLs): ISAba1-bla(OXA-23) (OXA-23-like; n = 7), ISAba3-bla(OXA-58)-ISAba3 (OXA-58-like; n = 2) and bla(OXA-72) (OXA-24-like; n = 6). The isolates were classified into 21 pulsotypes using PFGE, and the representative 15 isolates were found to belong to sequence type ST2 of the Pasteur MLST scheme from the global IC2 clone. The Oxford MLST scheme revealed the diversity among these studied isolates, and identified five sequence types (ST195, ST208, ST208/ST1806, ST348 and ST425). CHDL-type carbapenemases and insertion elements upstream of the bla(CHDL) genes were found to be widespread among Polish A. baumannii clinical isolates, and this contributed to their carbapenem resistance.