Whole genome sequencing insight into carbapenem-resistant and multidrug-resistant <i>Acinetobacter baumannii</i> harboring chromosome-borne <i>bla</i> _OXA-23

Carbapenem-resistant <i>Acinetobacter baumannii</i> (CRAB) poses a significant threat to hospitalized patients as effective therapeutic options are scarce. Based on the genomic characteristics of the CRAB strain AB2877 harboring chromosome-borne <i>bla</i>_OXA-23, which was isolated from the bronchoalveolar lavage fluid (BALF) of a patient in a respiratory intensive care unit (RICU), we systematically analyzed antibiotic resistance genes (ARGs) and the genetic context associated with ARGs carried by CRAB strains harboring chromosome-borne <i>bla</i>_OXA-23 worldwide. Besides <i>bla</i>_OXA-23, other ARGs were detected on the chromosome of the CRAB strain AB2877 belonging to ST208/1806 (Oxford MLST scheme). Several key genetic contexts associated with the ARGs were identified on the chromosome of the CRAB strain AB2877, including (1) the MDR region associated with <i>bla</i>_OXA-23, <i>tet(B)-tetR(B</i>), <i>aph(3'')-Ib,</i> and <i>aph(6)-Id</i> (2); the resistance island AbGRI3 harboring <i>armA</i> and <i>mph(E)-msr(E</i>) (3); the Tn<i>3</i>-like composite transposon containing <i>bla</i>_TEM-1D and <i>aph(3')-Ia</i>; and (4) the structure "IS<i>Aba1-bla</i>_ADC-25." The first two genetic contexts were most common in ST195/1816, followed by ST208/1806. The last two genetic contexts were found most frequently in ST208/1806, followed by ST195/1816.IMPORTANCEThe <i>bla</i>_OXA-23 gene can be carried by plasmid or chromosome, facilitating horizontal genetic transfer and increasing carbapenem resistance in healthcare settings. In this study, we focused on the genomic characteristics of CRAB strains harboring the chromosome-borne <i>bla</i>_OXA-23 gene, and the important genetic contexts associated with <i>bla</i>_OXA-23 and other ARGs were identified, and their prevalent clones worldwide were determined. Notably, although the predominant clonal CRAB lineages worldwide containing the MDR region associated with <i>bla</i>_OXA-23, <i>tet(B)-tetR(B</i>), <i>aph(3'')-Ib,</i> and <i>aph (6)-Id</i> was ST195/1816, followed by ST208/1806, the CRAB strain AB2877 in our study belonged to ST208/1806. Our findings contribute to the knowledge regarding the dissemination of CRAB strains and the control of nosocomial infection.