Comparative Analysis of Acinetobacter baumannii Bloodstream Isolates from Children and Adults in Southern China

Fen Xue¹Hui Xu¹Nan Gao¹Cheng Li¹Fan Fei²Rui Zhao¹Tiantian Zhang¹Liangxia Liang²Xing Wang³Yanfeng Zhao^1,4*Xingran Du^2*

• ¹The Second Affiliated Hospital of Nanjing Medical University, Nanjing, China
• ²The Affiliated Jiangning Hospital of Nanjing Medical University, Nanjing, China
• ³Shanghai Children's Medical Center Affiliated to Shanghai Jiaotong University School of Medicine, Shanghai, China
• ⁴Nanjing Medical University, Nanjing, China

Acinetobacter baumannii (A. baumannii ) is a major pathogen responsible for hospital-acquired bloodstream infections, with multidrug-resistant (MDR) strains posing severe therapeutic challenges. Neonates are particularly vulnerable to these infections, often associated with high morbidity and mortality. In this study, 77 blood isolates of A. baumannii from children (n=42) and adult (n=35) sources were subjected to comparative genomics and phenotypic analysis. Fourteen antimicrobial resistance assays were performed on the isolates, and antimicrobial resistance genes and virulence genes of the isolates were analysed and MLST typed using whole genome sequencing (WGS), and a phylogenetic tree of single-nucleotide polymorphisms (SNPs) in the core genome of the strains was constructed. We investigated key antibiotic resistance mechanisms, including β-lactamase production and multidrug efflux pumps, as well as virulence factors, such as pore proteins, lipopolysaccharides, metal-acquisition systems, and virulence secretion systems. The study results showed that the carbapenem antibiotic resistance rate of pediatric isolates (97.6%) was significantly higher than that of adult isolates (65.7%). In addition, adult isolates were more diverse in OXA-type carbapenemases. Virulence factor analysis revealed widespread distribution of porins, lipopolysaccharide synthesis genes, metal acquisition system, and type VI secretion system components in both groups, and virulence and resistance genes showed a higher detection rate in child isolates. A. baumannii were primarily ST2 (89.6%), all of which contained the blaOXA-23 gene. The survey also showed that ST466 and ST57 were only found in adult strains.These analyses will enhance our understanding of the mechanisms of A. baumannii resistance in different age groups and provide timely empirical drug therapy and adoption of infection control strategies.