676 STREPTOCOCCUS 



TABLE 37 



Group and Type Specific Antigens of Hemolytic Streptococci (modified from 



Lanobfield 1941). 



The association between the type of polysaccharide and the hsemolytic power 

 of the organisms is variable. So far as we know, most Group A strains give rise 

 to typical ^-haemolysis on blood agar plates ; but as already pointed out a few 

 strains have been reported that are heemolytic only under anaerobic conditions, 

 or are frankly non-haemolytic. In human infections we are generally on safe 

 ground in disregarding non-haemolytic streptococcal colonies ; except under very 

 unusual conditions, they are unlikely to be responsible for the ordinary manifesta- 

 tions of hsemolytic streptococcal infections. In Group B, however, the position 

 is different. Stableforth (1932) found that about half the bovine strains he studied 

 were non-haemolytic, even though he could detect no immunological difference 

 between the hsemolytic and the non-hsemolytic members of the group. Among 

 the other groups, non-hsemolytic strains have been found with varying frequency. 

 Special strains in Group C produce a-hsemolytic colonies ; and one group, Group N, 

 comprising strains of Str. lactis, appears to give rise to uniformly non-hsemolytic 

 colonies. The evidence suggests that the possession of the group polysaccharide 

 is a more constant and fundamental character than the abiUty to lyse blood cells. 

 It is therefore becoming common to pay greater attention to the type of poly- 

 saccharide present in a given strain than to its hsemolytic power ; though in 

 practice, especially in medical laboratories, the observation of haemolysis con- 

 stitutes the first important differential criterion of presumptive pathogenicity. 



The polysaccharides themselves, which are sometimes referred to as " C " 

 substances, appear to form an integral part of the bacterial cell. To obtain them 

 in solution, the organisms have to be disrupted. For this purpose, either Lance- 

 field's (1933) acid-extraction method or Fuller's (1938) formamide method may 

 be used. Their presence can be demonstrated by a simple precipitation reaction, 

 using specially prepared antiserum. They seem to play no part in the agglutina- 

 tion of streptococci. There is little information yet on their chemical structure, 

 but the polysaccharide of Group A strains is known to yield reducing sugars on 

 hydrolysis, to be non-toxic for animals, and to be antigenic only when in combination 

 with the cellular protein. 



Type Relationships. 



Group A. — The findings recorded by Dochez, Avery and Lancefield (1919) 

 BUss (1920, 1922), Gordon (1921), Eagles (1924) and Stevens and Dochez (1926a, b) 



