44 



Scientific Proceedings (95). 



27 (1402) 



Carbohydrate fermentation by bacteria as influenced by the com- 

 position of the medium. 



By J. Bronfenbrenker and M. J. Schlesinger. 



[From the Department of Preventive Medicine and Hygiene, Harvard 

 Medical School, Boston, Mass.] 



The value of the fermentation test among the methods at our 

 disposal for identification of bacteria is generally accepted. And 

 yet, every bacteriologist must have encountered in his experience 

 a number of instances of apparently inexplicable inconsistencies 

 in the results obtained by this test. Not only does it often happen 

 that a given strain producing a large amount of acid or gas will 

 occasionally produce very little, but at times indeed it produces 

 none at all. In fact, the amount of gas produced by a bacterium 

 at different times varies so widely, that at present it is suggested 

 by some bacteriologists that the amount of gas produced by a 

 given culture has no diagnostic significance. This point of view 

 owes its existence merely to the fact that the amount of gas pro- 

 duced by a given culture has no diagnostic significance. This 

 point of view owes its existence merely to the fact that the amount 

 of gas produced by bacteria depends on too many factors to at- 

 tempt to control them. In our work we came across inconsis- 

 tencies in the amount of acid and gas production, but discovered 

 that these inconsistencies were very often due to variations in the 

 composition of the media. The study is indeed not finished, but 

 even in its present stage it is quite convincing. Omitting the 

 details of the experiment, which will be published in full later, we 

 shall state here merely the general plan and the results obtained. 



The experiment consisted in growing a strain of B. coli, which, 

 in the original culture, produced very little acid or gas, upon a 

 medium consisting of peptone-phosphate-lactose-water with the 

 addition of an indicator permitting direct reading of hydrogen 

 ion concentration developed in the growing culture. 1 The com- 

 position of this medium was varied in every possible direction. 



1 This indicator, consisting of China blue and rosolic acid, was described by us in 

 the September issue of the Journal of Medical Research. 



