Outbreak of Multidrug-Resistant (MDR) Acinetobacter baumannii ST-15 Strains Co-producing OXA-23 and OXA-58 in South America

Abstract Acinetobacter baumannii is a high-priority pathogen due to its global dissemination and antimicrobial resistance. This work describes the first report of A. baumannii ST-15 isolates belonging to the International Clone 4 group, that exhibited an MDR profile with the co-production of OXA-23 and OXA-58 enzymes. Strains were isolated from an intensive care unit in a hospital of the Brazilian Amazon. Eight strains were recovered from an intensive care unit, showing high clonal stability across diverse clinical sources, including tracheal aspirates, urine, and blood, which underscores the high versatility and systemic dissemination potential of this lineage.The bla OXA−23 and bla OXA−58 genes were detected in all strains. A. baumannii isolates AB_OXA58_IEC07 and AB_OXA58_IEC02 were selected for hybrid genome sequencing and plasmid reconstruction, respectively, as representative samples of the outbreak. The reconstructed mobilome revealed a genome size of 4,110,050 bp, a GC content of 39.2%, and 3846 coding sequences for the reference strain, while four distinct plasmids were fully resolved.The bla OXA−58 gene was detected flanked by IS Aba 3 and IS6-like elements. p dif modules were identified in another plasmid, together with mobilization and replication genes. The tet39 gene was also identified in a novel plasmid that is likewise mobilizable. VFDB found several genes related to biofilm formation and virulence. The identification of these high-risk genetic determinants within a monoclonal outbreak, involving diverse clinical sites, emphasizes the successful persistence of the ST-15 lineage in the hospital environment. This study describes a rare co-production of oxacillinases, highlighting the importance of constant genomic surveillance in monitoring the emergence of antibiotic-resistant pathogens that could pose a threat on a regional or global scale.