MLST Typing Improves Streptococcus suis Diagnosis

The use of MLST typing is helping diagnosticians more accurately distinguish pathogenic Streptococcus suis isolates from those that are avirulent or commensal. Streptococcus suis is a bacteria that lives in pigs throughout the world but not all Strep suis will cause disease, making diagnosis a challenge.

Dr. Matheus Costa, an Assistant Professor with the Western College of Veterinary Medicine and an Adjunct Professor at Utrecht University, says diagnosticians and veterinarians have typically used serotyping to categorise Strep suis isolates according to the protective capsule that surrounds them but, with the popularization of genetic sequencing, we can obtain the whole genome opening the door to the further identification of markers specially associated with virulence.

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

Serotyping is what we call a phenotypic characterization.That means we're looking at the bacterial cell capsule, which is a sort of shield that the cell has.MLST is actually a genetic characterization.

We're looking on the genome of Strep suis and asking if the genome related or does it resemble another virulent Strep suis or not?Within a serotype, for example serotype 2, we have multiple different MLST types and not all of them can cause disease in pigs.

We can have a serotype 2 and expose or infect pigs with a serotype 2 and those pigs do not develop any kind of disease and some other serotypes 2 can actually induce very severe disease.The difference between those two isolates is not phenotypic, it's not the serotype, it's not their capsule or shield.

It's actually a genetic difference that is identified by MLST.So MLST is providing us with a closer look, a higher resolution at strep suis and how we can use that to differentiate between virulent and avirulent or commensal strains.

Dr. Costa stresses we should not stop doing serotyping but rather combine serotyping with MLST typing to help us further profile Strep suis.