Cross reactivity among the swine mycoplasmas as identified by protein microarray

- The genes for surface antigens of Mycoplasma hyopneumoniae were cloned, sequence modified, expressed in E. coli and purified.
- Protein microarrays were printed and rabbit hyperimmune sera used to interrogate them.
- M. hyopneumoniae and M. flocculare were similar in their reactivity, whereas M. hyosynoviae demonstrated few cross-reactive antigens and M. hyorhinis none.

Mycoplasmas are cell wall-less bacteria that infect a variety of animals in a species-specific manner. In swine, Mycoplasma hyopneumoniae is the most virulent and presents the most disease and economic problems to the swine industry. Serological assays are commonly used to assess colonization and disease, but antigenic cross-reactivity between M. hyopneumoniae and other mycoplasma species, most notably Mycoplasma hyorhinis, Mycoplasma hyosynoviae and Mycoplasma flocculare, is a concern. The extent of cross-reactivity has not been thoroughly investigated. These studies were designed to identify M. hyopneumoniae proteins that are recognized by rabbit hyperimmune sera raised against the other swine mycoplasmas. Our results indicate extensive cross-reactivity between M. flocculare and M. hyopneumoniae, which explains previous reports seen with ELISA assays. Only three of the thirty-nine M. hyopneumoniae proteins tested showed no cross reactivity with the other three swine mycoplasmas, mhp182 (42 kDa C-terminal fragment), mhp638 and mhp684 (C-terminal fragment). Two proteins, mhp384 and mhp511, were cross-reactive with hyperimmune sera generated against three of the four species. None of the anti-M. hyorhinis hyperimmune sera reacted to any of the M. hyopneumoniae proteins. These results suggest that inapparent M. flocculare infections could produce positive responses in M. hyopneumoniae serological assays due to cross-reactivity, and that M. hyosynoviae infections are less likely to do so and M. hyorhinis infections unlikely to affect assay results.