Separation and Characterization of Individual Mycolic Acids in Representative Mycobacteria

Total mycolic acid methyl ester fractions were isolated from 24 representatives of Mycobacterium tuberculosis, Mycobacterium bovis (including BCG), Mycobacterium microti, Mycobacterium kansasii and Mycobacterium avium. The total mycolate functional group composition was estimated from (1)H-NMR spectra. Mycolates were separated into alpha-mycolates, methoxymycolates and ketomycolates and each class was further separated by argentation chromatography into mycolates with no double bonds, with one trans-double bond and with one cis-double bond. Mass spectrometry revealed the mycolate chain lengths and (1)H-NMR the cis- and trans-double bond and cyclopropane ring content. The same species had similar mycolate profiles; the major type of each class had cis- or trans-cyclopropane rings and lacked double bonds. Minor proportions of possible unsaturated precursors of the cyclopropane mycolates were commonly encountered. Among unusual alpha-mycolates, many strains had tricyclopropyl components with chains extended by 6 to 8 carbons. Significantly, M. tuberculosis (Canetti) and M. avium had alpha-mycolates with a trans-double bond and cyclopropane ring, whose chain lengths suggested a relationship to possible precursors of oxygenated mycolates. The methoxy- and ketomycolates from a majority of M. tuberculosis strains had minor amounts of components with additional cyclopropane rings, some of whose chains were also extended by 6 to 8 carbons. These latter mycolates were major components in the attenuated M. tuberculosis H37Ra strain, whose mycolate profile was distinct from those of other strains of M. tuberculosis.