Emergence of NDM-1 and OXA-23 Co-Producing <em>Acinetobacter baumannii</em> ST1 Isolates from a Burn Unit in Spain

The global emergence of carbapenem-resistant Acinetobacter baumanii (CRAB) represents a significant public health threat. In the summer of 2002, a polyclonal CRAB outbreak occurred in our hospital, marking the first detection of an NDM-1 plus OXA-23 co-producing A. baumannii strain in Spain. The aim of this study was to phenotypically and genotypically characterize the clonal spread of NDM-1 and OXA-23 co-producing A. baumannii isolates and to describe the infection control measures implemented to contain the outbreak. Patients with multidrug-resistant A. baumannii isolates (July 2022-May 2023) were included in the study. Isolates were identified by MALDI-TOF and antimicrobial susceptibility was tested using a broth microdilution method (DKMGN SensititreTM panels). Whole genome sequencing was performed on 24 representative isolates. Phylogenetic analysis was performed using Ridom SeqSphere+ (cgMLST), while sequence typing was performed using ARIBA (Pasteur and Oxford schemes). A. baumannii isolates from the affected patients belonged to five different sequence types. The two main STs were ST1Pas/ST231Oxf (NDM-1 and OXA-23 co-producing), which accounted for 58%, and ST136Pas/ST406Oxf (OXA-23 producing), which accounted for 21%. All isolates were resistant to fluoroquinolones, trimethoprim/sulfamethoxazole, aminoglycosides and carbapenems. In addition, 8% were resistant to colistin and 17% to cefiderocol. Finally, the affected patients were cohorted and a thorough cleaning of the affected units was carried out. This study documents a clonal spread of an NDM-1 and OXA-23 co-producing A. baumannii strain in Spain, linked to a Libyan patient, highlighting the risk of cross-border spread. Although infection control measures successfully contained the outbreak, surveillance is essential as the incidence of CRAB infections is expected to increase.