A novel intranasal mouse model for mucosal colonization by Streptococcus suis serotype 2

Streptococcus suis causes meningitis and various other diseases in pigs and humans. Healthy piglets carrying virulent Streptococcus suis strains on their mucosal surfaces are epidemiologically very important. The objective of this study was to establish an intranasal Streptococcus suis mouse model for invasion and colonization of the respiratory tract. CD1 mice were infected intranasally with a highly virulent Streptococcus suis serotype 2 strain under different conditions. Clinical, histological and bacteriological screenings revealed that invasion of host tissue occurred in the majority of mice only after predisposition with 12.5 µl 1 % acetic acid per nostril. Severe fibrinosuppurative or purulent necrotizing pneumonia associated with Streptococcus suis was a common manifestation. Furthermore, a novel model to study nasopharyngeal colonization was established by reducing the volume of 1 % acetic acid per nostril to 5 µl prior to Streptococcus suis application. This model mimics asymptomatic carriage in swine, as all mice carried Streptococcus suis on their respiratory mucosa at 7 days post-infection (p.i.) in moderate to high numbers without the development of pneumonia or any other invasive Streptococcus suis disease. This intranasal Streptococcus suis model was applied to investigate the function of suilysin (SLY) in colonization. Although an isogenic SLY mutant was isolated from the upper respiratory tract at a lower recovery rate than its wild-type parental strain at 14 days p.i., the differences were not significant and did not indicate severe attenuation in colonization. In conclusion, this work describes to the best of our knowledge the first intranasal mouse model to study colonization of the respiratory tract by a highly virulent Streptococcus suis pathotype.