THE HEMOLYTIC STREPTOCOCCI : GROUP A 579 



Properties, Classification and Nomenclature of the Hsemolytic Streptococci 



Before describing the pathogenicity of the various streptococci, it will be con- 

 venient to summarize the main properties of the different groups, and to discuss 

 the nomenclature of the organisms within each group. It must be emphasized 

 once again that not all strains falling into Lancefield's groups form /5-haemolytic 

 colonies on blood agar. The heading of this section is not strictly accurate ; but 

 until some more suitable term is proposed we shall include a-haemolytic and non- 

 hsemolytic organisms possessing the same group polysaccharide as hsemolytic 

 organisms under the general designation of hsemolytic streptococci. 



Group A. 



Streptococci belonging to this group share in common the Group A carbohydrate com- 

 ponent described by Lancefield. They are divisible into a number of different serological 

 types, either by agglutination reactions with absorbed sera, or by precipitin reactions 

 carried out with type-specific antisera and suitably prepared bacterial extracts. The 

 type-specific antigens concerned are protein in nature, and soluble in dilute acids. Of the 

 27 types described by Griffith (1935), it would appear that four (Types 7, 20, 21 and 16) 

 do not possess the group-specific carbohydrate, and should therefore be excluded from this 

 group. Types 7, 20 and 21 belong, antigenically, to Group C ; Type 16 to Group G (Hare 

 1935). 



Group A streptococci, in addition to producing /S-hsemolysis in blood agar plates, appear, 

 without exception, to form a soluble hsemolysin. 



In regard to their other biological and biochemical characters. Group A streptococci 

 produce a final pH of 5-0-5-6 in dextrose broth ; they do not hydrolyse sodium hippurate ; 

 they do not reduce methylene blue in milk ; they ferment trehalose but not sorbitol ; they 

 may or may not grow in 10 per cent, bile agar, and seldom grow in 40 per cent, bile agar. 

 These are the main differential group characters. In addition. Group A strains almost 

 always ferment salicin and lactose, seldom mannitol, and very seldom raffinose or inuHn. 

 With the exception of Type 3 strains (FuUer and Maxted 1939, Hadley et al. 1941), peroxide 

 is generally produced. A biochemical classification, based on the fermentation of starch, 

 mannitol, and cellobiose, which is in concordance with serological typing, has been pro- 

 posed by Keogh and Simmons (1940). 



The strams that have been adequately identified as belonging to this grouji have, in 

 the main, been derived from infections in man — tonsillitis, scarlet fever, cellulitis, erysipelas, 

 puerperal fever, other types of septicaemia, acute broncho-pneumonia, otitis media and so 

 on. They have also been isolated from the throat, nasopharynx, or nose, in normal persons. 

 They have occasionally been isolated from cases of mastitis in cattle ; but in such instances 

 there have usually been grounds for suspecting a human som-ce of infection. 



It is clear that streptococci falling into Group A possess all the characters that 

 have been attributed to the classical Str. pyogenes ; and the group itself is so well 

 differentiated that it clearly requires a distinctive label. Should it be given specific 

 rank ? It is certain that we cannot include in a single species all the antigenic 

 groups of hsemolytic streptococci (A-N). The only question is, into how many 

 different species they should be divided. The balance of the evidence at present 

 available appears to us to be in favour of recognizing the Group A strains as con- 

 stituting a species in the generally accepted bacteriological sense. Its relation to 

 the strains falling into other antigenic groups will be discussed in succeeding sections. 

 There remains the question of the correct specific name. The name Str. hcemohjticus 

 has obtained wide currency. It was used by the Committee of the Society of 

 American Bacteriologists to denote the type species (Winslow et al. 1920), and we 

 adopted it in the first edition of this book. 



