Establishment and application of an indirect ELISA for the detection of antibodies to porcine Streptococcus suis based on a recombinant GMD protein

Streptococcus suis ( S. suis ) is an important zoonotic pathogen from sick and recessive carrier pigs, which poses a serious threat to animal husbandry production and public health. It usually causes horizontal transmission among pigs and the morbidity and mortality of this disease are very high. Human infection is caused through direct or indirect contact with sick pigs. The two large-scale outbreaks of S. suis in China were due to the outbreak of S. suis on pig farms, which spread to human infection, so its detection of S. suis pig herds is very important. This study developed an indirect ELISA (SS-GMD-ELISA) for the detection of S. suis antibody. The antigen-antibody response was optimized by checkerboard titration. The results of testing by ELISA for salmonella enterica, Escherichia coli and staphylococcus aureus were all negative, indicating that this method had strong specificity. The results were still positive when the dilution ratio of S. suis positive serum reached 1:6,400, indicating that the method had high sensitivity. Repeatability test results showed that the intra-assay coefficient of variation and the inter-assay coefficient of variation were less than 10% ,indicating that the method had good repeatability. The seroprevalence of S. suis in 167 serum specimens collected in eastern China was also investigated and 33.5% of the samples evaluated positive for anti- S. suis IgG antibodies, indicating that the seroprevalence of S. suis was high in pig populations in China, The new SS-GMD-ELISA was a convenient, sensitive and specific diagnostic method, which provided technical support for the rapid diagnosis, epidemiological investigation and prevention and evaluation of vaccines.