Analysis of virulence and immunogenic factors in Aeromonas hydrophila: Towards the development of live vaccines

• Published in: Journal of fish diseases 2020-07, Vol.43 (7), p.747-755
• Main Authors: Zhao, Xian‐liang, Wu, Gan, Chen, He, Li, Li, Kong, Xiang‐hui
• Format: Article
• Language: English
• Subjects: Aeromonas hydrophila; Aeromonas hydrophila - pathogenicity; Aeromonas hydrophila - physiology; Animals; Aquatic environment; Bacterial Vaccines - immunology; Cyprinus carpio; Deoxyribonucleic acid; Disease control; DNA; DNA vaccines; Fish; Fish diseases; Fish Diseases - immunology; Fish Diseases - microbiology; Fish Diseases - prevention & control; Freshwater fishes; Genes; Genotype & phenotype; Genotypes; Gram-Negative Bacterial Infections - immunology; Gram-Negative Bacterial Infections - microbiology; Gram-Negative Bacterial Infections - prevention & control; Gram-Negative Bacterial Infections - veterinary; Hemorrhagic disease; Immunogenicity; Immunologic Factors - immunology; live vaccine; Outer membrane proteins; Pathogenesis; Pathogenicity; Pathogens; Strains (organisms); Vaccines; Vaccines, Attenuated - immunology; Virulence; Virulence factors
• ISSN: 0140-7775; 1365-2761
• DOI: 10.1111/jfd.13174

Aeromonas hydrophila, a bacterium that is widespread in aquatic environments, is responsible for causing haemorrhagic disease in both aquatic and terrestrial species. With the purpose of developing a live vaccine, herein we have investigated nine strains of A. hydrophila (Ah‐01 to Ah‐09) isolated from diseased fish. A study of virulence factors that contribute to pathogenicity and immunogenicity in the host Cyprinus carpio suggests that the presence of β‐hly, act and fla genes contribute to pathogenesis: strains Ah‐01, Ah‐02 and Ah‐03 (β‐hly+/act+/fla+ genotype) were highly pathogenic to C. carpio, whereas Ah‐05 and Ah‐06 (β‐hly−/act−/fla− genotype) showed weak pathogenicity. Accordingly, Ah‐02 and Ah‐03 were selected to prepare inactivated vaccines, whereas Ah‐05 and Ah‐06 were chosen as live vaccines. Ah‐06 live vaccine was found to have the best protective efficacy, with a protective rate of about 85%, whereas rates of other vaccines were significantly lower, in the range 37%–59%. In addition, DNA vaccines based on genes altA, aha and omp showed immune protection rates of 25%, 37.5% and 75%, respectively. Our data demonstrate that the β‐hly−/act−/fla−/altA+/aha+/omp+ genotype has weak pathogenicity and high immunogenicity, and provide a simple and effective way to screen for live A. hydrophila vaccines.