Phenotypic and Genotypic Characterization of Carbapenem-Resistant Acinetobacter baumannii in Intensive Care Units in Lagos State

Carbapenem-resistant Acinetobacter baumannii (CRAB) has emerged as a priority critical pathogen, with its capacity for sustained healthcare environmental persistence and extensive drug resistance posing existential threats to ICU infection management in Nigeria. This analytical study phenotypically and genotypically characterized CRAB isolates from ICU patients across Lagos Island General Hospital and Lagos University Teaching Hospital, Lagos State, in the South West geopolitical zone of Nigeria. Clinical isolates of A. baumannii recovered from respiratory secretions, blood, and wound samples from 90 ICU patients were identified by MALDI-TOF mass spectrometry. Carbapenem susceptibility was assessed by broth microdilution. Carbapenemase gene detection was performed by multiplex PCR targeting OXA-23-like, OXA-24-like, OXA-58-like, NDM-1, IMP, and VIM genes. Sixty-seven percent of A. baumannii isolates were carbapenem-resistant. OXA-23-like genes were detected in 91.5 percent of CRAB isolates, representing the dominant resistance mechanism. NDM-1 co-production was confirmed in 21.3 percent of OXA-23-positive isolates. All CRAB isolates demonstrated resistance to at least six antibiotic classes. Colistin retained in-vitro activity against 84 percent of CRAB isolates. Molecular typing by REP-PCR revealed two dominant clonal clusters circulating across both ICUs. These findings document the clonal dissemination of OXA-23 CRAB in Lagos ICUs and advocate for colistin-based combination regimens, enhanced environmental decontamination, and ICU-level molecular surveillance. Keywords: Acinetobacter baumannii, carbapenem resistance, OXA-23, ICU, Lagos.