UNITED STATES DEPARTMENT OF AGRICULTURE 
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 alkali-forming groups of 
bacteria 2 
Cause of the 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 alcohcls 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 
HISTORICAL 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) 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 
i The numbers in parentheses refer to " Literature cited " at end of bulletin. 
104410°— 19— Bull. 782 1 
