Characterization of an Attenuated Aeromonas hydrophila Vaccine and Molecular Mechanisms of Channel Catfish Immunity against Aeromonas hydrophila infection

Abstract

An attenuated Aeromonas hydrophila AL09-71 N+R vaccine strain was compared to its virulent parent strain A. hydrophila AL09-71. The attenuated AL09-71 N+R strain was developed through selection of resistance to both novobiocin and rifampicin. The attenuated AL09-71 N+R strain had smaller colony size, slower growth and weaker chemotactic response compared to AL09-71. The motility and invasion ability of AL09-71 N+R were found to be abolished whereas that of AL09-71 was retained. The fatty acid methyl ester profiles of the attenuated strain AL09-71 N+R were detected to be different from that of AL09-71. However, at genomic DNA level, AL09-71 N+R appeared to be similar to that of AL09-71. To understand the molecular mechanisms of protection elicited by the attenuated AL09-71 N+R vaccine strain in catfish, suppression subtractive hybridization (SSH) was used to identify genes up-regulated by the vaccine. A total of 22 unique genes were identified at 12 h post vaccination. Of the 22, six were confirmed to be significantly induced by vaccination. In addition, 88 channel catfish genes that were reported to be associated with host immunity were included in the expression analysis. Of the 88 genes, 14 were found to be significantly up-regulated by the vaccination. Expression profiles of the 20 genes at different time points showed that the pattern of gene up-regulation in vaccinated fish was similar to that in infected fish. To understand whether channel catfish response to secondary infection is similar to primary infection, SSH was used to identify genes up-regulated by secondary infection. Of the 28 unique genes identified by the library, eight were confirmed to be significantly induced by secondary infection compared to that by primary infection at 6 h post infection. In addition to the eight genes identified by SSH, 94 genes known to be associated with host immunity were also subjected to expression analysis. Of the 94 genes, 22 were identified to be induced and differential regulated at different time points. These results suggest that channel catfish host response play an important role in its immunity against A. hydrophila infection.