Genotypic and phenotypic diversity of Streptococcus dysgalactiae strains isolated from clinical and subclinical cases of bovine mastitis

This study was conducted to characterize Streptococcus dysgalactiae isolated from cases of bovine mastitis. One hundred strains from 100 dairy herds in Denmark, 29 strains from 29 dairy herds in Pennsylvania, USA, 7 reference strains and 18 strains consisting of 9 paired strains from 9 quarters were investigated using biotyping (utilization of tagatose and sorbitol) and HindIII ribotyping. Four different biotypes were observed. Only 34 of the 100 Danish strains utilized either tagatose or sorbitol, 18 utilized tagatose, 15 sorbitol and 1 both tagatose and sorbitol. In contrast, among the American strains one (3.4%) did neither utilize tagatose or sorbitol, twenty (69.0%) utilized tagatose, four (13.8%) sorbitol and four (13.8%) both tagatose and sorbitol. HindIII ribotyping produced 15 different types among all the strains, 9 different types were found among the Danish strains and 8 types among the American strains. Five types were observed among both the Danish and the American strains. The 7 reference strains were assigned to 5 different ribotypes. Three type strains (ATCC 27957, NCTC 4670, NCTC 4335) were assigned to a type that was present among both the Danish and the American strains. Ribotyping was the most discriminatory typing method. Agreement between ribo- and biotyping was observed, and especially pronounced among the Danish strains. The 9 paired strains were in each case found to have identical ribo- and biotype.