Analysis of virulence proteins in pathogenic Acinetobacter baumannii to provide early warning of zoonotic risk

Acinetobacter baumannii is a ubiquitous opportunistic pathogen usually with low virulence. In recent years, re-ports of increased pathogenicity of A. baumannii in livestock due to the migratory behaviour of wildlife have attracted public health attention. Our previous study reported that an A. baumannii strain isolated from dead chicks, CCGGD201101, showed enhanced pathogenicity, but the mechanism for increased virulence is not un-derstood. Here, to screen potential virulence factors, the proteomes of the isolated strain CCGGD201101 and the standard strain ATCC19606 of A. baumannii were compared, and the possible virulence-enhancing mechanisms were further analysed. The 50 % lethal dose (LD50) values of CCGGD201101 and standard strain ATCC19606 in ICR mice were determined to verify their bacterial toxicity. 2D fluorescence difference gel electrophoresis (2D-DIGE) combined with matrix-assisted laser desorption/ionization time of flight mass spectrometry (MALDI-TOF/ TOF-MS) and quantitative real-time PCR (RT-qPCR) were applied to screen and identify differentially expressed proteins or genes that may be related to virulence enhancement. Bioinformatics analyses based on protein- -protein interaction (PPI) networks were used to explore the function of potential virulence proteins. The path-ogenicity of potential virulence factors was assessed by phylogenetic analyses and an animal infection model. The results showed that the LD50 of CCGGD201101 for mice was 1.186 x 106 CFU/mL, and the virulence was increased by 180.5-fold compared to ATCC19606. Forty-seven protein spots were significantly upregulated for the A. baumannii CCGGD201101 strain (fold change >= 1.5, p < 0.05). In total, 14 upregulated proteins were identified using proteomic analysis, and the mRNA expression levels of these proteins were nearly identical, with few exceptions. According to the PPI network and phylogenetic analyses, the I78 family peptidase inhibitor, 3-oxoacyl-ACP reductase FabG, and glycine zipper were screened as being closely related to the pathogenicity of bacteria. Furthermore, the I78 overexpression strains exhibited higher lethality in mouse infection models, which indicated that the I78 family peptidase inhibitor was a potential new virulence factor to enhance the pathoge-nicity of the A. baumannii CCGGD201101 strain. The present study helped us to better understand the mecha-nisms of virulence enhancement and provided a scientific basis for establishing an early warning system for enhanced virulence of A. baumannii from animals.

Automated summary

This study compared the proteomes of A. baumannii strains and identified potential virulence factors associated with enhanced pathogenicity through protein-protein interaction network analysis, phylogenetic analysis, and animal infection models. The results showed that the pathogenicity of strain CCGGD201101 was increased by 180.5-fold compared to the standard strain. The study helps to better understand the mechanisms of virulence enhancement.