The context of blaOXA-23 gene in Iraqi carbapenem-resistant Acinetobacter baumannii isolates belonging to global clone 1 and global clone 2.

Background and objectives: Of the genes conferring resistance to carbapenems in Acinetobacter baumannii, the bla_OXA-23 gene is the most widely found across the world. The gene carrying bla_OXA-23 transposons in A. baumannii isolates of global clones GC1 and GC2 is found worldwide. Here, we examined whether transposons play a role in the dissemination of the bla_OXA-23 in globally distributed clones, GC1 and GC2 A. baumannii isolates from Iraq.

Materials and methods: The 119 non-repetitive A. baumannii isolates including 94 recovered from clinical specimens and 25 isolates from hospital environment between September 2021 and April 2022 from different medical centers located at various regions in Baghdad, Iraq. The global clones (GC) and the genes encoding carbapenem resistance, including bla_OXA-23, bla_OXA-24, and bla_OXA-58 were identified using multiplex PCR assays. Antibiotic susceptibility testing was performed by the Kirby-Bauer disk diffusion susceptibility method. The transposons carrying bla_OXA-23 were examined using PCR mapping. In cases when carbapenem susceptible A. baumannii isolates were found, they were subjected to E test, full length sequencing of bla_OXA-Ab (bla_OXA-51-like) and Institut Pasteur multi-locus sequence typing scheme.

Results: All but two isolates (92 clinical and 25 environmental) were identified carbapenem-resistant A. baumannii (CRAB). Of 117 CRAB isolates, 20 belong to GC1, 19 contained bla_OXA-23; of them, 17 isolates harbored the bla_OXA-23 located on Tn2006. Among the 46 CRAB belonging to GC2, 39 contained bla_OXA-23; of them, 34 carried the bla_OXA-23 located on Tn2006. The remaining GC1 and GC2 isolates, one GC1 as well as one GC2 isolate, were susceptible to imipenem, doripenem, and meropenem and considered carbapenem-susceptible A. baumannii (CSAB). Full-length sequencing of the bla_OXA-Ab and MLST for the two CSAB isolates belonging to GC1 and GC2 confirmed that the GC1 isolate belongs to ST 623 and contained an allele that encodes an bla_OXA-69 variant of the bla_OXA-Ab while the GC2 belong to ST2 and carried an bla_OXA-66 variant.

Conclusion: This study provides evidence for the dissemination of bla_OXA-23 on the Tn2006 in CRAB isolates in Baghdad, Iraq. It appears that this transposon is widespread in GC1 and 2 isolates as in the other parts of the world. Interestingly, one GC1 and one GC2 isolate from Iraq were found to be susceptible to carbapenem while the isolates belonging to GC1 and GC2 have so far rarely been found to be susceptible to carbapenem globally.