Screening of antagonistic bacteria against Flavobacterium columnus and its effects on growth performance and immune function of Carassius auratus

Abstract

With the popularization of modern intensive farming models, aquatic animals are more prone to outbreaks of various diseases. Due to the abuse of antibiotics, drug resistance among pathogenic bacteria and the deterioration of the water environment continue to occur. Therefore, it is essential to find probiotics that can effectively resist the erosion of pathogenic microorganisms, enhance fish's immunity, and promote fish's growth as an alternative to antibiotics.In this experiment, two strains of probiotic bacteria antagonistic to Flavobacterium columnar were isolated from pond water samples. They were identified as Bacillus amyloliquefaciens and Acinetobacter johnsonii by 16S rRNA gene sequence analysis. To further analyze the physiological function of the two probiotics, we added Bacillus amyloliquefaciens, Acinetobacter johnsonii and two strain mixtures to the base feed and fed crucian carp separately. The results found that after 40 days of feeding, the growth performance of wild crucian carp and total protein(TP), globulin(GLO), albumin(ALB) and total bile acid(TBA) had no significant effect. However, Bacillus amyloliquefaciens could significantly reduce total bilirubin(TBiL), direct bilirubin(DBiL), indirect bilirubin(IBiL) and hypersensitive C-reactive protein(hs-CRP) in the serum of crucian carp. The addition of Acinetobacter johnsonii significantly reduced the content of indirect bilirubin(IBiL), acetonitrile/glutamate(A/G) and hs-CRP in the serum of wild crucian carp, which could effectively increase the range of superoxide dismutase(SOD) and reduce the production of malondialdehyde(MDA). After adding the mixed bacteria, Immunoglobulin M(IgM) in the serum of wild crucian carp increased significantly. In addition, the detection of intraperitoneal injection at 24 h, 48 h and 96 h was found to have no significant effect on the serum biochemical indicators of wild crucian carp.The above results show that adding Acinetobacter johnsonii can enhance crucian carp's anti-inflammatory, immunity and antioxidant properties. Therefore, the two bacteria can be used as potential probiotics for wild crucian carp. The research on this topic is of great significance for the screening of water probiotics, improving the water environment, optimizing the intestinal flora of fish, and improving the immunity of fish. At the same time, it provides new ideas for promoting healthy fish farming.