The Combination of β-Glucan and Astragalus Polysaccharide Effectively Resists Nocardia seriolae Infection in Largemouth Bass (Micropterus salmoides)

Effectively treating and preventing outbreaks is crucial for improving the economic benefits of aquaculture. Therefore, utilizing immunostimulants, either alone or in combination, is regarded as a promising strategy. In this study, beta-glucan + APS (200 mg/kg + 200 mg/kg), beta-glucan (200 mg/kg), APS (200 mg/kg), enrofloxacin (15 mg/kg), and sulfadiazine (15 mg/kg) were added to feed to assess the effects against Nocardia seriolae infection in largemouth bass (Micropterus salmoides) within 14 days. The survival rates did not differ between the enrofloxacin group and the beta-glucan + APS group, but both were significantly higher than that of the control group. Additionally, the enrofloxacin group and the beta-glucan + APS group exhibited the lowest bacterial loads and tissue damage. Importantly, the beta-glucan + APS treatment significantly improved serum enzyme activities (total superoxide dismutase, lysozyme, total protein) and the expression of immune genes (IL-1 beta, TNF-alpha, IFN-gamma, IgM) compared to the other treatment groups. The enrofloxacin group showed similar efficacy to the beta-glucan + APS group in combating N. seriolae infection, but N. seriolae in the enrofloxacin group developed drug resistance. In summary, the combined use of beta-glucan and APS is a promising strategy for treating bacterial diseases, thereby contributing to the promotion of sustainable aquaculture development.

Automated summary

This study evaluated the effects of different immunostimulants added to feed on Nocardia seriolae infection in largemouth bass. The results showed that the combined use of beta-glucan and APS significantly improved survival rates, reduced bacterial loads and tissue damage, and enhanced immune indicators. The combined treatment demonstrated promising efficacy in treating bacterial diseases in aquaculture.