680 STREPTOCOCOUS 



But tlie knowledge that has accumulated during recent years seems to us to 

 render the name inconvenient and misleading. If we adhered to it, we should 

 no longer mean by Str. hcemolyticus a " hsemolytic streptococcus," or even a " strepto- 

 coccus giving i^-hsemolysis," but only a particular group of streptococci falling 

 into that category. It therefore seems to us wiser to revert to the name Str. pyogenes, 

 defining that name as equivalent to " a streptococcus of Group A," with the proviso 

 that this definition may well have to be modified in the future. 



Before leaving this group and turning to others we may note briefly the existence of 

 certain strains that have been isolated from milk and from the throats of infected persons 

 during milk-borne epidemics of tonsiUitis (Davis and Rosenow 1912, Davis 1912, 1929, 

 Stokes and Hachtel 1912, Capps and Davis 1914). These streptococci differ from the class- 

 ical Str. pyogenes only in giving mucoid or semi-mucoid colonies on blood agar plates and 

 in showmg well-defined capsules. Because of this difference Davis allotted to them a 

 separate specific name, Str. epidemicus. It seems very doubtful, however, whether this 

 procedure is justified. Although Str. pyogenes is not a capsulated species in the same 

 sense as Str. pneimwnice, it not infrequently forms recognizable capsules when growing in 

 the tissues, or during the first few hours of its growth in serum broth. Seelemann and 

 Hadenfeldt (1932) compared a large number of strains bearing the label Str. epidemicus 

 with typical strains of Str. pyogenes, and were unable to distinguish between them. On 

 the basis of the available evidence we think that the name Str. epidemicus should be pro- 

 visionally discarded, and that the strains bearmg that label should be included in the 

 species Str. pyogenes. It may be noted that there is some tendency for other organisms 

 to produce capsules when growing in milk. 



Similarly, there seems to us no adequate reason for allotting different specific names to 

 strains that, while possessing all the essential characters of Str. pyogenes, differ from one 

 another in regard to certain fermentation reactions. We should not, therefore, recognize 

 a Str. infrequens, fermenting mannitol as well as sahcm, or a Str. anginosus fermenting 

 neither of these sugars. It is, indeed, by no means certain that all the strains to which these 

 names have been attached are true hsemolytic streptococci of the pyogenes type. 



Group B. 



The streptococci of this group share in common a group-specific antigen that is carbo- 

 hydrate in nature and differs from the group-specific antigen of Group A, or of any of the 

 groups subsequently described. Group B streptococci are further divisible by precipita- 

 tion or agglutination tests into four main antigenic types, and by absorption of agglutinin 

 tests into a number of sub-types. The type-specific antigens within this group are appar- 

 ently not acid-soluble proteins, but complex carbohydrates of a different chemical structure 

 from the carbohydrate that determines group-specificity. 



Streptococci falling within this group may or may not produce yS-hsemolysis in blood 

 agar plates. It would appear (see Stableforth 1932) that something over hah" of these 

 strams are /3-hsemolytic ; but the exact proportion is still a subject of controversy. Brown 

 (1937, 1939) has shown that the hsemolytic strains are characterized by the formation 

 of a double zone of haemolysis, which is best seen around deep colonies m rabbit blood 

 agar incubated for 48 hours at 37° C. and refrigerated overnight. Although many haemo- 

 lytic Group B strains yield a soluble hsemolysin, it would seem that this character is much 

 less constant than with Group A strains ; and the titres of the filtrates obtained are 

 usually much lower. 



In regard to their other biological and biochemical characters, Group B strains dififer 

 from Group A strains in that they produce a lower final pH in glucose broth (4-2-4-8), 

 hydrolyse sodium hippurate, and usually grow both on 10 per cent, and 40 per cent, bile 

 agar. They resemble Group A strains in faihng to reduce methylene blue in mUk, and in 

 fermenting trehalose but not sorbitol. Sucrose and glycerol are usually fermented (Sim- 

 mons and Keogh 1940, Gunsalus and Sherman 1943), but mannitol, raflfinose, sorbitol, 



