Enzyme-linked immunosorbent assay for the detection of antibodies against the extracellular domain of the OxaA membrane protein of Mycoplasma suis

Epidemics of swine infected with Mycoplasma suis, a hemotrophic pathogen, cause substantial economic losses to the swine industry worldwide. The complementary DNA sequences encoding two predicted extracellular domains of the OxaA protein of M. suis were obtained using polymerase chain reaction and standard molecular cloning methods. The OxaA domains were expressed separately in Escherichia coli as glutathione-S-transferase (GST) fusion proteins, designated as GST-A and GST-B. The antigenicity of the GST-A and -B recombinant proteins was confirmed by western blotting. The GST-A and -B proteins were approximately 33.9 kDa and 34.6 kDa in size, respectively. An enzyme-linked immunosorbent assay (ELISA) was developed for the detection of antibodies against the OxaA protein of M. suis using the GST-B protein. The efficacy of the GST-B-based ELISA was compared to a previously described ELISA method based on the analysis of serum samples from 150 swine, and the M. suis-positive rates were 22.7% and 17.3%, respectively. The GST-B-based ELISA demonstrated significantly higher levels of specificity, sensitivity, and stability for the serodiagnosis of M. suis infection in swine than those of the previously described method.