Abstract:

Glaesserella parasuis (GPS) is one of the important pathogenic bacteria in pigs, and serotype identification has been a long-standing "bottleneck" in the field of GPS research since it was identified as the causative agent of Glasser's disease in pigs in 1910. In 1992, the gel immunodiffusion(GID) typing method based on GPS heat-stable antigens classified GPS as 1-15 for the first time, but about 25% of the strains were not typed, and the composition of the typed antigen was not clear at that time. In 2003, an indirect hemagglutination assay (IHA) typing method for GPS-based "saline extract" antigen was established, and its sensitivity and typing rate were higher than those of GID, but about 15% of the strains were still untypeable. The typing results of IHA and GID methods are generally identical, so it is possible to determine whether the typed antigens are based on the same GPS surface polysaccharide composition, but it is still not certain whether it is a capsular polysaccharide, or LPS, or even other polysaccharide species. In 2013, the synthetic gene cluster of GPS serotype 1-15 capsular polysaccharide was successfully analyzed, which confirmed that the essence of serotype antigen formation was capsular polysaccharide. In 2015, Howell et al. designed primers based on the specific target genes of GPS capsule, and established a PCR typing method for GPS (H-PCR), but it could not distinguish serotype 5 and 12. In 2017, Jia et al. also established a set of PCR typing methods (J-PCR) for specific target genes based on GPS capsule, which could identify serotypes 5 and 12. The combination of the two PCR typing methods was able to type almost all GPS strains, and their consistency with the GID and IHA methods was verified from molecular biology, and the antigen basis of the three typing methods was finally confirmed to be GPS capsule. The PCR typing method has the advantages of simple operation, fast speed and low cost, and has successfully solved many problems in GID and IHA serotyping methods, and has been widely used. In this paper, we systematically reviewed the history of the establishment and application of GPS GID, IHA and PCR typing methods, as well as the discovery process of the same antigen basis, in order to provide systematic theoretical knowledge for the immunological material basis and principle of the three GPS typing methods, and to provide new ideas for the research and development of Glasser's disease prevention and control technology.

Key words: Glaesserella parasuis, capsule, serotype, gel immunodiffusion (GID), indirect hemagglutination assay (IHA), PCR