Acinetobacter baumannii is a challenging pathogen and a major epidemiological threat responsible for healthcare-associated infections and increasing multidrug resistance, including to last-resort agents such as polymyxins. This study aimed to characterize carbapenem- and polymyxin-resistant A. baumannii clinical isolates from a state hospital in Rio de Janeiro.

Between September and December 2024, nine A. baumannii isolates resistant to carbapenems and polymyxin B were received at LabSUR from ICU patients of a state hospital. Carbapenemase genes were screened by multiplex PCR. Clonal relatedness was assessed by pulsed-field gel electrophoresis (PFGE). A representative isolate of the predominant clone underwent whole-genome sequencing (WGS), analyzed through the CABGen pipeline.

All isolates were positive for blaOXA-23 and blaOXA-51 genes. The nine polymyxin-resistant isolates belonged to the same clonal group, six from tracheal secretions and three from surveillance swabs, originating from seven ICU patients (two patients with duplicate samples). Five patients occupied the same ICU beds at different times; two patients died. The sequenced representative strain belonged to sequence type 1 (ST1), a high-risk clone linked to outbreaks and global dissemination of resistance genes. The isolate also harbored aminoglycoside- and sulfonamide-resistance genes and mutations in pmrB and lpxC associated with polymyxin resistance.

The results suggest persistence and circulation of a clonal A. baumannii lineage resistant to carbapenems and polymyxin B within a hospital unit, belonging to a high-risk clone. These findings reinforce the importance of continuous monitoring, control of clonal dissemination, and targeted interventions to mitigate its impact on public health.