Abstract
BACKGROUND: Multidrug-resistant Acinetobacter baumannii (MDR-AB) poses a critical threat in neonatal intensive care units (NICUs), however few studies have reported the molecular characterization of A. baumannii isolates from the NICU in China. This study aims to describe the molecular, biofilm and motility characteristics related to carbapenem resistance genes in A. baumannii isolates from the NICU. METHODS: Following an outbreak in March-April 2024, 21 A. baumannii isolates from neonatal and environmental sources were collected. These isolates underwent antimicrobial susceptibility testing, whole-genome sequencing (WGS) for resistance gene profiling and multi-locus sequence typing (MLST). Biofilm formation and twitching motility were measured in representative strains exposed to subinhibitory concentrations of gentamicin, levofloxacin, and meropenem. RESULTS: All 21 A. baumannii isolates were carbapenem-resistant Acinetobacter baumannii (CRAB), showing resistance to cephalosporins, aminoglycosides, and quinolones. WGS identified 25 resistance genes, including the universal bla (OXA-23), bla (OXA-66), bla(ADC-25) and bla (TEM-1D), aminoglycoside resistance genes (armA, aph genes), macrolide resistance genes (mphE, msrE), and tetracycline (tetB) resistance genes. Efflux pumps (adeABC, adeFGH, adeIJK) were ubiquitous. Two sequence types emerged: ST195 (20 isolates) and ST1959 (1 isolate), with high genetic similarity suggesting nosocomial transmission. ST1959 exhibited stronger biofilm formation than ST195. Biofilm formation of ST1959 was significantly enhanced by gentamicin but inhibited by levofloxacin. Meropenem suppressed only the ST195 biofilms. Twitching motility was markedly reduced in ST1959 and also decreased after levofloxacin exposure. CONCLUSION: This NICU outbreak was driven by CRAB ST195 harboring a conserved resistome. Strain-specific differences in biofilm formation and motility under antibiotic stress highlight the interplay between genetic lineage and phenotypic adaptability. Levofloxacin demonstrates dual anti-biofilm and anti-motility effects, which could guide targeted infection control strategies against high-risk A. baumannii clones.