Capacity of Group A, B, C, D and G Streptococci to Agglutinate Sensitized Sheep Red Cells

The reactivity of streptococci with sheep red cells, sensitized with a subagglutinating dose of rabbit anti‐sheep red cell antibodies was studied; agglutination of sensitized and not non‐sensitized sheep red cells by streptococci was demonstrated in isolates belonging to groups A, B, C, D and G. The frequencies of isolates which had the capacity to agglutinate were 97, 88 and 100 per cent in group A, C and G, but only 47 and 33 in group B and D. The agglutination of sensitized sheep red cells by streptococci diminished after treatment of the streptococci with protease from Streptomyces griseus , but was not affected by pepsin or trypsin treatment. Heating the streptococci at 60°C for 30 minutes and repeated subculturing did not suppress their agglutinating activity. Besides, various streptococcal extracts agglutinated sensitized sheep red cells. The presence of an immunoglobulin G reactivity in streptococci might cause certain difficulties in the serological grouping and typing of streptococci.