UNITED STATES DEPARTMENT OF AGRICULTURE 



jXf^''^'m/'U 



i BULLETIN No. 782 |^» 



Contribution from the Bureau of Animal Industry 

 JOHN R. MOHLER, Chief 



Washington, D. C. 



PROFESSIONAL PAPER 



June 17, 1919 



A STUDY OF THE ALKALI-FORMING BACTERIA 

 FOUND IN MILK. 



By S. Henry Ayers, Philip Rupp, and Wm. T. Johnson, Jr., 

 of the Dairy Division, Bureau of Animal Industry. 



CONTENTS. 



Historical review 1 



Definition of the aUcali-forming groups of 



bacteria 2 



Cause of tlie alkaline reaction in milk 3 



Sources of the alkali-forming bacteria 9 



Morphology and growth 10 



Sources of nitrogen 11 



Fermentation of carbohydrates 12 



Fermentation of alcohols 17 



Fermentation of salts of organic acids 19 



Reduction of nitrates and nitrites 30 



Arbitrary grouping of the alkali-forming 



bacteria from milk 33 



Summary and conclusions 35 



fflSTORICAL REVIEW. 



Occasionally references to the alkali-forming bacteria are found 

 in bacteriological literature. This group of bacteria has not received 

 much attention, probably because under the ordinary conditions of 

 plating their presence can not be detected, and as a consequence 

 their rather wide distribution has been overlooked. 



The fact that alkali-forming bacteria are often present in market 

 milk in large numbers was first brought to the attention of the 

 authors during some studies (1) ^ on the bacteriology of raw and pas- 

 teurized milk. At that time no suitable means were available for 

 obtaining any exact figures on their numbers in market milk, so they 

 were classed with the inert types of bacteria. Wolff (12) in a study 

 of bacteria which developed in milk found nonliquefying short rods, 

 colonies of which resembled those of the colon-aerogenes group. 

 These organisms were strict aerobes which produced neither acid nor 

 gas but turned milk alkaline without any other change. Shippen (10) 

 also found organisms, in the milk supply of Baltimore, which gave an 

 alkaline reaction in milk without peptonizing or coagulating it. He 

 found that these organisms in cultural reactions closely -resembled 



1 The numbers in parentheses refer to "Literature cited " at end of bulletin, 

 104410°— 19— Bull. 782 1 



