Factors Concerned in Demonstrating Utilization of Carbohydrates by Organisms of the Genus Mycobacterium.

Abstract

In plain broth cultures of organisms of the genus Mycobacterium I have shown that the method of incubation definitely affects the reaction changes produced. Cultures sealed from the atmosphere were shown to produce only slight growth with an accompanying slight drop in the pH of the media. This slight growth was shown to be due to lack of oxygen and the slight reaction change to the acid side has been shown to be due to production and retention of carbon dioxide. Cultures not sealed from the atmosphere were shown to become progressively alkaline.

Reaction change determinations, using a modification of the method of Long and Major, 1 upon mannite, galactose, and dextrose broth cultures of 9 organisms of this genus showed only 3 outstanding variations from the plain broth control. These 3 were as follows: Myco. leprae and Myco. phlei in mannite broth and Myco. chelonei in dextrose broth.

These results, as well as others, showed definitely that the primary change in reaction is not to the acid side when these organisms are grown in carbohydrate broth. The suggested explanation of the peculiarly characteristic action of organisms of this genus when grown in carbohydrate broth was that these organisms utilize the carbohydrates completely, no cleavage products remaining in the media. This characteristic is undoubtedly closely associated with the strict aerobic nature of these organisms. It was concluded that the method of determining carbohydrate utilization by noting the appearance of acid in the media, which is the method generally used for such determinations, is not applicable to the determination of carbohydrate utilization by organisms of the genus Mycobacterium.

Furthermore, the reaction curves are influenced to such a slight degree by the addition of carbohydrates to the plain broth, regardless of whether or not the carbohydrates are utilized, that reaction curve determinations constitute an indefinite and impracticable method of determining carbohydrate utilization by organisms of this genus.