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Five species of Mycobacterium were analyzed for the fatty acid composition of total and neutral lipids and of individual classes of phosphatides. The methyl esters of fatty acids were analyzed using the technique of gas liquid chromatography. It was found that myristic, palmitic, palmitoleic, and tuberculostearic acids were the major fatty acids present in all of the lipid components of these strains of tubercle bacilli. The ratio of unsaturated to saturated fatty acids is lowest in the most pathogenic strain, indicating a progressive increase in this ratio, and the highest ratio is represented by a saprophytic strain. An avian pathogenic organism falls in the center of this classification among the examined strains of mycobacteria. These results indicate that the ratio of unsaturated to saturated fatty acids of lipids can be used to determine and establish the pathogenic species of mycobacteria.

A comparative study was undertaken of lipid composition of Mycobacterium tuberculosis H(37)Rv and H(37)Ra, M avium, M phlei, and M 607. Neutral lipids and phosphatides constituted about 55 and 25 percent of the total lipids, respectively. Seven different phosphatides were isolated and identified in varying proportions in all of the above species of mycobacteria. These were polyglycerophosphatide, phosphatidic acid, phosphatidylethanolamine, lysophosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol dimannoside, and phosphatidylinositol pentamannoside. Choline-containing phosphatides and cholesterol (steroids) were not detected in lipids of any of the five species under these defined experimental culture medium and growth conditions. Interestingly enough, neutral lipids of M tuberculosis (H(37)Rv and H(37)Ra) contained a higher percentage of diglycerides than monoglycerides, whereas in the other species (M avium, M phlei, and M 607) the monoglyceride content exceeded that of the diglycerides. It appears that the lipid composition of mycobacteria can be an additional useful parameter in distinguishing pathogenic from nonpathogenic species of mycobacteria.