Study on the Optimization of Medium Composition to Increase the Viable Counts of Streptococcus suis Type 2 NT15B Strain
[Objective]The experiment took Streptococcus suis type 2 NT15B strain as the research object.By optimizing the fermentation medium components,the viable counts of the strain was increased and the production cost was reduced,so as to provide a reference for high-density culture of Streptococcus suis type 2 NT15B strain and the research related to the large-scale production and promotion of the vaccine against porcine streptococcal disease.[Method]The maximum viable counts of Streptococcus suis type 2 NT15B strain was used as the screening index,and the optimal components and concentrations of carbon sources,nitrogen sources(organic and inorganic nitrogen sources),inorganic salt metal ions,and phosphoric acid buffers in the fermentation medium of the strain were screened by single-factor test.According to the results of single factor screening,3 levels of each of 4 factors,carbon source concentration,total organic nitrogen source concentration,organic nitrogen source proportion and phosphate buffer concentration,were selected to design orthogonal tests,and further multi-factor screening and verification were carried out.[Result]The optimal fermentation medium of Streptococcus suis type 2 NT15B strain was 6.0 g/L sucrose,1.0 g/L urea,10 g/L yeast extract YE7 mixed with 20 g/L yeast peptone Nucel 887 as nitrogen sources,1.0 g/L NaCl,9.58 g/L K2 HPO4·3H2O,1.09 g/L KH2PO4,1 mmol/L MgSO4·7H2O and 0.3 g/L L-ascorbic acid.Using this optimal combination,the viable counts of Streptococcus suis type 2 NT15B strain at the shaking flask level was 80.83×108 CFU/mL,which was 256.08％higher than before optimization.[Conclusion]The optimized medium effectively increased the viable counts of Streptococcus suis type 2 NT15B strain,reduced production costs and provided a reference for optimization in fermenters.
Streptococcus suis type 2viable countsmedium compositionoptimization
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