Effects of intranasal challenge with group A beta haemolytic streptococcus M type 49 in Swiss albino mice

Mice are susceptible to natural infections with streptococci and therefore can serve as suitable animal models to study experimental streptococcal infections. In an earlier study, we had shown the development of pharyngeal colonization, antibody response and histopathological changes in the heart following intranasal (IN) challenge with a rheumatogenic serotype of group A beta haemolytic streptococcus, the M type 18. To determine if nonpharyngitis associated serotypes can also elicit similar responses, 30 Swiss albino mice were challenged intranasally with 2 x 10(7) colony forming units of a skin associated serotype of group A beta haemolytic streptococcus, the M type 49. Pharyngeal colonization varied from 64% (n = 30) in the first week to 69% (n = 16) during the fourth week after IN challenge. Eleven (36.7%) of the 30 animals studied showed antibody response to DNase B (ADNB) with peak titers varying from 150 to 1200 units. Wide variations were seen in ADNB titers in individual mice. Histopathological evidence for cardiac lesions were seen in three animals. The changes were mild and varied from mild to chronic endocardial inflammation to calcification. The study shows that Swiss albino mice are also susceptible to IN challenge with skin associated strains of GABHS and therefore can serve as useful models to study the effects of experimental infection with diverse serotypes of GABHS.