598 STREPTOCOCCUS 



type, and the growth seldom or never becomes evenly diflfuse. There is no peUicle forma- 

 tion. 



On gelatin the growth is slight, and the colonies are minute and punctiform. 



In gelatin stab there is a sUght growth along the track, with minimal growth on the 

 surface. The gelatin is not liquefied. 



On potato growth is very slight, and often not detectable by the naked eye. 



Heat Resistance, and Viability. — Str. pyogenes is killed by heating to 55° C. for 

 30 minutes. It tends to die out in subculture unless preserved under particularly favourable 

 conditions, but it remains viable for long periods in the dry state. 



Biochemical Reactions. — Str. pyogenes does not hydrolyse sodium hippurate ; does 

 not reduce methylene blue in milk ; produces a final pH of 5 0-5 -6 in glucose broth ; 

 ferments trehalose, lactose, saccharose, salicin and occasionally mannitol, with the formation 

 of acid but no gas ; does not ferment sorbitol, inulin or raffinose. Produces acid in litmus 

 milk, but no coherent clot. Does not liquefy gelatin. Does not reduce nitrates. Does 

 not form indole. Is not soluble in bile. Its growth is inhibited by bile. 



Antigenic Structure. — Str. pyogenes possesses the group-specific polysaccharide 

 antigen of Lancefield's Group A hsemolytic streptococci. It is differentiated into a large 

 number of antigenic types by type-specific protein antigens ; over 30 of these types have 

 so far been identified by agglutination and absorption and by precipitation tests. 



Pathogenicity and Toxin Production. — Str. pyogenes produces a variety of infections 

 in man, and more rarely in domestic animals. Some strains are highly pathogenic for the 

 mouse or the rabbit, less so for the guinea-pig. It produces a soluble haemolysin, a leuco- 

 cidin, an erythrogenic toxin and a fibrinolysin acting on human fibrin. 



Str. agalactise 



Morphology, Growth Requirements and Type of Growth. — In these characters 

 Str. agaladice does not differ significantly from Str. pyogenes ; in many strains, however, 

 the cells are yellow or red in colour. 



Action on Blood. — Between one-third and one-half of the strains of Str. agalactice 

 that have been examined produce /S-heemolysis in blood agar plates. These strains produce 

 a filtrable hsemolysin of the oxygen-stable type. 



Heat Resistance. — Str. agalactice is killed by heatmg to 60° C for 30 minutes. 



Biochemical Reactions. — Str. agalactice hydrolyses sodium hippurate ; it does not 

 reduce methylene blue in milk ; it produces a final pH of 4-2-4-8 in glucose broth ; it 

 produces acid in trehalose, sucrose, glycerol, and usually in lactose and sahcin, but not 

 in sorbitol, mannitol, rafiinose or inuhn ; it forms acid and clot in milk ; it does not hquefy 

 gelatin. It is not soluble in bile. Its growth is not inhibited by 10 per cent, bile, and 

 usually not by 40 per cent. 



Antigenic Structure. — Str. agalactice possesses the group-specific polysaccharide 

 antigen of Lancefield's Group B streptococci. It is separable into different antigenic 

 types, four of which have so far been identified, by type-specific antigens which appear 

 to be carbohydrate, not protein in natiu-e. Sub-types of the foiu- main types have been 

 recognized. 



Pathogenicity and Toxin Production. — Str. agalactice is an important cause of 

 mastitis in cattle. Its pathogenicity for laboratory animals is low. Some, if not all, 

 strains produce a filtrable hsemolysin. It does not produce a fibrinolysin acting on human 

 fibrin. Whether it produces a leucocidin is unknown. There is no evidence that it produces 

 an erythrogenic toxin. 



Str. pneumoniae 



Morphology. — Ovoid or lanceolate cocci, arranged in pairs or short chains ; when 

 in pairs, the adjacent ends of the cocci are usually bluntly rounded, the opposite ends 



