Genomic Characterization of Carbapenem-Resistant Acinetobacter baumannii in ICU Environments: Mobile Genetic Elements, Efflux Pumps, and Resistance Mechanism

Bing Wang,1,2 Weiran Wang,1,2 Min Lu,1,2 Hui Jin1,2 1Department of Disinfection Surveillance and Vector Control, Hangzhou Center of Disease Control and Prevention (Hangzhou Health Supervision Institution), Hangzhou, Zhejiang, People’s Republic of China; 2Zhejiang Key Laboratory of Multi-Omics in Infection and Immunity, Hangzhou Center of Disease Control and Prevention (Hangzhou Health Supervision Institution), Hangzhou, Zhejiang, People’s Republic of ChinaCorrespondence: Hui Jin, Hangzhou Center of Disease Control and Prevention (Hangzhou Health Supervision Institution), No. 568 Mingshi Road, Shangcheng District, Hangzhou, Zhejiang, 310021, People’s Republic of China, Tel +86-571-85177602, Email [email protected]: To investigate the genomic resistance profile of carbapenem-resistant Acinetobacter baumannii (CRAB) isolates from ICU environments, with a focus on characterizing a representative CRAB strain I2 to elucidate its genomic determinants of resistance and assess their implications for infection control.Methods: Between 2012 and 2015, a total of 24 Acinetobacter baumannii strains were isolated from high-touch surfaces ICUs of four hospitals. Antimicrobial susceptibility testing against 15 antibiotics was performed for all isolates using the VITEK® 2 system. One representative strain was selected for whole-genome sequencing. Resistance genes, virulence factors, and mobile genetic elements were systematically analyzed using bioinformatics tools and databases. In addition, the biofilm formation capacity of this strain was quantitatively assessed by crystal violet staining.Results: Resistance rates to β-lactams ranged from 58.33% to 66.67%, while 95.83% of isolates remained susceptible to polymyxin. The representative CRAB strain I2 (sequence type 191) harbored three carbapenemase genes and 13 ade efflux pump genes, with 40 resistance genes identified (68.75% efflux-mediated). Genomic island GI16 (carrying transposase ISAba1) suggested horizontal gene transfer driving resistance dissemination. A total of 99 virulence genes and disinfectant resistance genes were detected. Biofilm formation capacity was moderate. Genomic analysis of strain I2 revealed a comprehensive resistance profile and potential mechanisms underlying environmental persistence and transmission.Conclusion: The ICU environment constitutes an important reservoir for CRAB. The strain I2 harbored key resistance determinants, including efflux pump, and mobile genetic elements, which correlated with its carbapenem-resistant phenotype. Additionally, this strain harbors biofilm-associated genes and disinfectant efflux pump genes, and exhibits moderate biofilm-forming capacity, indicating strong environmental adaptability. The genomic characteristics of strain I2 provide a molecular basis for implementing targeted CRAB infection control strategies in high-risk healthcare settings.Keywords: Acinetobacter baumannii, carbapenem resistance, genomic islands, biofilm, infection control