In recent years, the frequent outbreaks of various bacterial infectious diseases are considered primary constraints and continuous challenges to the development of aquaculture industry. As an effective method of preventing a wide range of bacterial diseases, vaccination has been playing a key role in aquaculture disease control for decades, contributing to its environmental, social, and economic sustainability. In particular, vaccines based on inactivated bacterial pathogens have proven highly effective for fish.   

After millions of years of coevolution, symbiotic microbiota has become an integral part of fish and plays an important role in fish immunity, metabolism, and health. Given the ability of vaccines to enhance immune function, the fish intestinal microbiota is likely an important, underappreciated factor in vaccine development. However, so far, minimal is known about the effect of vaccination on fish symbiotic microbiota, especially mucosal microbiota, and its correlation with intestinal metabolism remains unclear.   

Recently, a research team led by Prof. LI Aihua from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences illustrated the effect of vaccination on tilapia symbiotic microbiota and found that significant alterations of intestinal symbiotic microbiota mediated changes in intestinal metabolism. This study was published in Microbiome.   

Using 16S rRNA gene high-throughput sequencing and gas chromatography-mass spectrometry metabonomics, the researchers compared the differences in the gill and gastrointestinal microbiota and intestinal metabolites of tilapia between the control and immunized groups. The results showed that vaccination had a significant effect on the structure and composition of intestinal mucosa-associated microbiota, but had no significant effect on the gill and stomach mucosa- and gastrointestinal digesta-associated microbiota.   

In addition, the researchers found that the contents of serum globulin and lysozyme, globulin ratio, the activity of superoxide dismutase, and the antibody titer were significantly higher in the immunized group than those in the control group. The relative abundance of potential opportunistic pathogens such as Aeromonas in the intestinal mucosae of tilapia in the immunized group was significantly reduced. Given that the gut is the main route for most pathogenic bacteria to infect fish, this protective mechanism of vaccines may be important.   

The researchers further discovered that the concentrations of carbohydrate-related metabolites, such as lactic succinic acid and gluconic acid, were significantly increased in the intestinal tract of the immunized group, while the concentrations of various metabolites related to lipid metabolism were significantly decreased in the intestinal tract of the immunized group.    

Correlation analysis showed that intestinal microorganisms, such as Enterovibrio, Macellibacteroides, Ralstonia, Pirellulaceae, Desulfomonile, Enhydrobacter, Crenothrix, and Bosea, were significantly correlated with differentiated intestinal metabolites after vaccination. These results suggested that vaccination affected the metabolic function of the tilapia gut, which was closely related to changes in gut microbes.   

This study revealed the microbial and metabolic responses induced by inactivated vaccination, suggesting that intestinal microbiota might mediate the effect of vaccination on the intestinal metabolism of tilapia. The intestinal microbes and metabolites that increased significantly after vaccination might serve as valuable indicators for probiotics or prebiotics development to enhance vaccine efficacy against vaccinated fish.  

(Editor: MA Yun)