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Highly selected group A streptococci, 108 strains isolated from different groups of individuals, were tested for binding of aggregated human IgG which had been pre-incubated in fresh human serum. All strains displayed resistance to phagocytosis typical of M-producing strains. Among 73 strains isolated from sporadic cases of acute glomerulo-nephritis (AGN), 34 (47 per cent) bound the aggregates. All of 26 type 12 group A streptococci but none of 15 type 49 strains proved positive in the test system. Furthermore, one type 1 and one type 18 strain were positive. All 9 type 49 strains isolated in a minor epidemic of AGN proved negative. Twenty-six strains of type 12 group A streptococci were isolated during three different prospective studies in which no cases of AGN had occurred; all these strains bound aggregates in the presence of fresh serum. Thus, it was found that the capacity to bind aggregates in the presence of fresh serum was strongly associated with — though not limited to — group A streptococci carrying the type 12 antigen. However, this characteristic is not common to all nephritogenic strains, since all type 49 group A streptococci were negative in the test system.

Group A streptococcal strains were isolated from the throats of 46 children suffering from scarlet fever. For detection of erythrogenic toxins (ETs), the culture supernatants were concentrated 100 times by ethanol precipitation and solubilisation in acetate buffer. ELISA was used to identify ETA and double immunodiffusion to identify ETB and ETC. The presence of the ETA gene was detected by a specific DNA probe. ETA (alone or in combination with ETB and/or ETC) was found in 51.9% of the strains, ETB (alone or in combination with ETA and/or ETC) in 76.9% and ETC (in combination with ETA and ETB) in 28.9%. Only 5.8% of strains did not produce any detectable ET. In SDS-PAGE, supernatants of ETB-producing strains showed a pronounced band in either the region of the proteinase zymogen or the active proteinase. There was no correlation between the type of erythrogenic toxin and the serological M or T type of the producing strain. The mitogenic potency of culture supernatants did not differ significantly irrespective of the toxin type(s) present. Culture supernatants of strains without a detectable amount of the known ETs were highly mitogenic, indicating the production of other streptococcal mitogens. A correlation with clinical symptoms was determined with regard to exanthema and fever. Strains producing two or three toxins caused a more intense exanthema. Patient temperature was higher (greater than or equal to 38 degrees C) when the infecting strain produced ETB. The toxin-producing patterns of the strains of this study were compared with those isolated during the last epidemic outbreak of scarlet fever in East Germany.