Pathogenicity and inactivated vaccine protection of Staphylococcus sciuri JS-1 on Carassius auratus

Staphylococcus sciuri is a common zoonotic pathogen to humans, animals and fish. It can cause a variety of diseases and a high fatality rate to aquatic animals. Carassius auratus is one of the most important aquaculture species in the world, and can be used as a good aquatic animal model. In order to explore the pathogenicity and inactivated vaccine protectivity of S. sciuri JS-1 on C. auratus, we designed the JS-1 injected infection experiment, the JS-1 supplemented feeding experiment, and the inactivated vaccine protection experiment, and samples were detected by histopathological observation, quantitative real-time PCR (qPCR) and enzyme activity detection. Results showed that in the JS-1 injected infection samples, C. auratus showed systemic hemorrhage, and its liver was congested and enlarged, and the 96-hour LD₅₀ was 5×10⁶ CFU/mL. In the JS-1 supplemented feeding experiment, the liver of C. auratus showed congestion and enlargement with irregular nucleus shape, the spleen was congested and had serious necrosis, the renal corpuscle was swollen and the space of renal capsule was enlarged, and the transaminase in serum increased at first and then decreased, and reached the highest level on day 14. The high concentration group showed the most obvious decrease trend, and the activity of lysozyme was significantly increased, compared with control group. On day 14, the lysozyme activity of the high concentration group was significantly higher than that of the control group (P<0.05), on day 28, the lysozyme activity of the low concentration group was significantly increased (P<0.05). The expression of TNF-α and IFN-γ genes in the liver and spleen of C. auratus increased at first and then decreased, and was significantly higher than that of the control group, and on day 21, the difference still existed. After injection of the inactivated vaccine, the activity of lysozyme in serum was significantly higher than that in the control group, while activities of alkaline phosphatase, transaminase, and superoxide dismutase were significantly lower than those in the control group, and the catalase activity was significantly increased; the specific IgM and total IgM in the serum immunized with inactivated vaccine were significantly higher than those in the control group. The content of specific IgM accounts for 50%-60% of the total IgM content, and the survival rate of crucian carp reached 83.3% on 10th day after JS-1 injection. This study showsed that S. sciuri JS-1 is highly pathogenic to C. auratus, causing systemic hemorrhage and internal organ damage, and inactivated vaccine of S. sciuri can stimulate the body to produce a strong immune response. The immune protection rate is more than 80%, and its inactivated vaccine can provide effective protection for C. auratus. This study provides a research basis for the development of S. sciuri vaccine.