Apr. 22, 1918 Streptococci Concerned in Cheese Ripening 



245 



sucrose with failure to ferment mannite and glycerin characterizes a 

 cheese streptococcus as a gas producer, for no strain which has fermented 

 this combination of test substances has failed to give a gas production 

 in peptone milk. The fermentation of raffinose by most strains also 

 distinguishes 5. kefir from S. laciicus and Streptococcus X. 



COMPARISON OF S. LACTICUS, STREPTOCOCCUS X, AND S. KEFIR 



5. laciicus, Streptococcus X, and 5. kefir are three well-defined species. 

 S. lacticus is characterized by a vigorous reduction of the litmus in milk 

 cultures, which precedes the curdling, and is complete beneath the pink 

 surface layer; about 0.12 gm. of acetic acid is produced per liter of milk; 

 crystals are formed in milk cultures by a large percentage of the strains; 

 and there is a vigorous production of alkali by the majority of strains 

 grown in peptone broth free of fermentable substance. Streptococcus X is 

 characterized by a slower production of acidity in milk cultures, with only 

 a partial reduction of the Htmus; no crystals are formed in milk cultures; 

 about 0.75 gm. of acetic acid is produced per liter of milk; and all strains 

 produce alkali in peptone broth. S. kefir is characterized by a faint 

 growth in milk cultures; no growth takes place in peptone broth; the 

 acetic acid production is similar to that of Streptococcus X; and there is a 

 vigorous production of gas in peptone milk or digested milk cultures. 



A summarized description of the three species of streptococci is given 

 in Table IV, where the characteristic reactions can be compared. Average 

 values are given in those columns of the table where the test is expressed 

 in numbers. Considering all the tests, the fermentation reactions gave 

 the least aid in this classification. The order of availability, however, 

 is distinctly different for each species, and there are certain individual 

 reactions which are more or less characteristic. For example, fermen- 

 tation of glycerin would indicate that a streptococcus belonged to the 

 Streptococcus X group; fermentation of raffinose would indicate that 

 a strain belonged to the 5. kefir group; fermentation of sucrose is also 

 somewhat characteristic of S. kefir, for it has been fermented by every 

 strain of this group, whereas the majority of strains of the other two 

 groups failed to ferment sucrose. 



Table IV. — Comparative description ofS. lacticus, Streptococcus X, and S. kefir 



"The minus sign (— ) indicates failure to form acids. 

 41154°— 18 3 



b Peptone was added to the milk. 



