We evaluated the kits for grouping β-hemolytic streptococci. Streptococcal Grouping Kit (Oxoid), which can identify the streptococci of Group A, B, C, D, G and F simultaneously, was superior to other kits which were tested. However, by using this kit, we found that Streptococcus pneumoniae has a cross-reactive antigen with Group C Streptococcus and the antigen may exist in the cell wall of S. pneumoniae.
We also measured MICs to gentamicin (GM) against clinical isolates of β-streptococci. The MICs of GM to Group A and B Streptococcus were relatively low (1.56-3.13μg/ml), whereas the MICs of the other groups of Streptococcus were higher than those of the former. These results indicated that susceptibility of β-hemolytic streptococci to GM is useful as one of the tests to identify β-hemolytic streptococci.
Furthermore, we studied the frequency of isolation of β-hemolytic streptococci from the clinical specimens. The results showed that frequency of isolation of Group F Streptococcus was higher than that of Group C and G Streptococcus from the clinical specimens, although it is previously said that most of the clinical isolates of β-hemolytic streptococcus were Group A, B, C or G.