Emergence and characteristics of hypervirulent Acinetobacter baumannii

This study aimed to characterize hypervirulent Acinetobacter baumannii (Hv-AB) strains and elucidate their clinical and microbiological profiles in a hospital setting. We conducted a retrospective analysis of 49 A. baumannii strains isolated from a Chinese hospital between July 2019 and June 2020. Strains were classified as Hv-AB or non-Hv-AB using Galleria mellonella infection models and survival curve analysis. Phenotypic assessments included antimicrobial susceptibility testing, serum resistance assays, biofilm formation quantification, and string tests. Among the 49 strains analyzed, 17 (34.7%) demonstrated hypervirulence (Hv-AB). These hypervirulent strains belonged to 9 distinct multilocus sequence typing(MLST) sequence types: ST191, ST195, ST208, ST381, ST540, ST1145, ST1474, ST1893, and ST2207. Phylogenetic analysis indicated that ST208 served as the founder sequence type (ST). Compared with ST208, ST191, ST195, ST540, ST1145, and ST1893 differed in only one housekeeping gene, classifying them as single-locus variants (SLVs); whereas ST381 and ST2207 differed in two loci, classifying them as double-locus variants (DLVs). Intensive Care Unit (ICU) is the main source for detecting high-virulence strains of A.baumannii. Hv-AB showed higher resistance rates to commonly used antibiotics, particularly sulfamethoxazole-trimethoprim, compared to non-Hv-AB. Patients with higher red blood cell counts or hemoglobin levels may be more susceptible to Hv-AB infection. No high viscosity of Hv-AB was found. Serum resistance and biofilm formation were not unique characteristics of Hv-AB. This study identifies the emergence of highly virulent Hv-AB strains in clinical settings and underscores their genetic homology. These findings contribute to a deeper understanding of Hv-AB.