NON-SPECIFIC PYOGENIC COCCI 



199 



litmus-lactose-agar plates is sometimes helpful, the colony appear- 

 ing surrounded by a zone of red. 



Growth occurs in most of the laboratory media, particularly 

 upon the addition of a sugar, such as dextrose. The colonies 

 upon agar and gelatin are small, rarely larger than a pinhead, 

 at first transparent, and almost dew-drop-like. Later they 

 may become somewhat opaque. The gelatin is not usually lique- 

 fied, although saprophytic strains are known which possess this 

 property. Whether these latter are typical 

 Streptococcus pyogenes is uncertain. Upon 

 agar slants this organism tends to grow in 

 the form of discrete colonies. Bouillon is 

 sometimes clouded by a uniform distribu- 

 tion of short chains; in other cases it 

 remains clear, the organism growing in 

 masses of long, tangled threads which 

 remain as a sediment at the bottom. 

 Blood-serum is unusually favorable as a 

 medium. A growth is frequently produced 

 upon the potato, though many strains 

 refuse to develop on this medium. Milk 

 is usually coagulated, with acid production 

 and no digestion of the curd. 



Physiology. Streptococcus pyogenes is 

 aerobic and facultative anaerobic. Its 

 optimum temperature is about 37, but 



growth will usually take place at room- 



* rpn xv. i j xv Fig. 86. Streptococ- 



temperatures. 1 ne thermal deatn-point cus pyogenes on a slant 



(Frankel 



differs in various strains usually about 60 

 for fifteen minutes is sufficient to destroy. 

 Antiseptics and disinfectants are efficient in destruction. No 

 pigment is produced. No coagulating or proteolytic enzymes are 

 developed in the typical strains, although, as indicated above, 

 gelatinase has been reported in some saprophytic types. No 

 indol is produced. No gas is developed in any medium. Acid 

 is produced by most strains from many sugars, particularly 

 dextrose and lactose. Efforts have been made to classify the 

 various types of Streptococcus on the basis of their acid-production 



