Isolation of Streptococcus suis using a selective medium

Area of Science:

• Veterinary Microbiology
• Bacteriology
• Animal Health

Background:

• Streptococcus suis is a significant swine pathogen.
• Accurate isolation and identification of S. suis are crucial for disease control.
• Current diagnostic methods may have limitations in sensitivity and specificity.

Purpose of the Study:

• To evaluate a novel selective medium for improved isolation of S. suis from porcine tonsillar tissue.
• To assess the concordance of S. suis capsular serotyping between two different laboratories.
• To identify limitations in the current serotyping scheme for S. suis.

Main Methods:

• A selective culture medium was formulated with tryptic soy agar, bovine blood, crystal violet, nalidixic acid, and gentamicin.
• Tonsillar samples from slaughtered pigs were cultured on the selective medium.
• Isolates were identified as S. suis and subjected to capsular serotyping.
• Serotyping results were compared between laboratories in Guelph and Copenhagen.

Main Results:

• The selective medium significantly improved the isolation rate of S. suis from tonsillar samples.
• Ninety-five percent of S. suis isolates were confirmed between laboratories.
• A notable discrepancy was observed in the confirmation of capsular serotype 2, with only 6 out of 21 isolates matching.
• A high percentage (64%) of S. suis isolates were not typable using the existing capsular serotyping scheme (serotypes 1-13 and 1/2).

Conclusions:

• The developed selective medium is effective for enhancing S. suis isolation from pig tonsils.
• There are significant challenges in consistent and accurate capsular serotyping of S. suis, particularly for serotype 2.
• The current capsular serotyping scheme is inadequate for a substantial proportion of S. suis isolates, necessitating further development.