Genetic Sequencing and MLST Typing Differentiates Between Pathogenic and Non-Pathogenic Strains of Strep Suis

The use of advanced genetic sequencing is allowing diagnosticians to determine the pathogenicity of Streptococcus suis.Serotyping has typically been used to categorise Strep suis isolates according to the protective capsule that surrounds the organism but serotyping does not differentiate between pathogenic and non-pathogenic isolates.

Dr. Matheus Costa, an Assistant Professor with the Western College of Veterinary Medicine and an Adjunct Professor at Utrecht University, says the advent of genetic sequencing provides the whole genome of the organism, opening the door to the identification of markers through MLST typing specially associated with virulence.

Clip-Dr. Matheus Costa-Western College of Veterinary Medicine:

Streptococcus suis is a bacteria that lives in the upper respiratory tract of pigs and many other places within the pig.We have found Streptococcus suis in the eyes of pigs, we have found it in their nasal cavities, in their throats and sows also have it inside their reproductive tract.

It's essentially living in close to 100 percent of the pigs.It's very hard to identify a pig that does not have Streptococcus suis.This doesn't mean these pigs are sick.This just means that Streptococcus suis can live with its host, which is pigs.

So, the challenge is, is Strep Suis the cause of disease or is Strep suis taking a ride on another agent, for example influenza virus or PRRS.Those viruses can open the door for bacterial infections so Strep suis would piggyback on that virus.

The virus prevents the immune reaction or destroys the epithelial lining and then Strep suis takes advantage of that situation and starts multiplying and you end up finding Strep suis.But, in that case, Strep suis is not the primary agent.It just happens to be there and takes that opportunity to grow and contribute to disease.

Dr. Costa says MLST typing is allowing diagnosticians to differentiate between virulent and non-virulent strains of Streptococcus suis at a genetic level.