Molecular analysis of carbapenem-resistant Acinetobacter baumannii isolated from bronchoalveolar lavage fluid in a tertiary hospital in Ningxia, China

Purpose Infections caused by clinical carbapenem-resistant Acinetobacter baumannii (CRAB) are associated with an increased risk of mortality and present a significant challenge for hospitals worldwide. This study aims to analyze the molecular epidemiological characteristics, drug resistance traits, and virulence features of CRAB isolated from bronchoalveolar lavage fluid (BALF) at a hospital in Ningxia, China. Methods We collected clinical characteristic data of patients with isolated strains and conducted statistical analysis. Antibiotic susceptibility testing was conducted using the VITEK-2 compact system. Carbapenemase and virulence genes were examined through PCR and Sanger sequencing. Multilocus Sequence Typing (MLST) was performed according to the Oxford MLST scheme by comparing the obtained sequences with known allele sequences available on the MLST website ( http://pubmlst.org/abaumannii/ ). The virulence of CRAB was assessed using the Galleria mellonella infection assay. Results The results indicated that all tested CRAB strains carried the bla OXA-23 and bla OXA-51 genes, exhibiting multidrug resistance characteristics while remaining sensitive to polymyxins. MLST typing revealed that ST195 and ST369 strains were the most prevalent, with several other types identified, including ST208, ST136, ST469, ST368, and a rare ST1779. Notably, 94.2% of CRAB belonged to Global clone 2. Significant clinical differences were observed between ST195 and non-ST195 infection cases. Virulence assessment results indicated that 71 strains (58.6%) exhibited high virulence characteristics. Additionally, virulence factors such as ompA, adeH, pgaA, abal, BasJ , and plcD were detected in all tested strains, confirming an evolutionary trend towards high virulence in CRAB, which poses a serious threat to clinical treatment and patient prognosis. Conclusion The emergence of highly virulent multidrug-resistant CRAB strains in the Ningxia region has increased a clinical burden, highlighting the importance of clinical surveillance and diagnosis of these strains.