Composition of mycolic acid molecular species as a criterion in nocardial classification

By using gas chromatography and gas chromatography-mass spectrometry, we analyzed the mycolic acid compositions of 18 strains of Nocardia asteroides, 17 strains of Nocardia farcinica, and 17 strains of Nocardia nova classified by numerical taxonomy. These organisms had characteristic mycolic acid compositions. We calculated the peak areas of the molecular species of mycolic acids on gas chromatograms and determined the average total carbon number in each strain. The strains of N. asteroides were divided into five groups, and the type strain belonged to group C-54. The strains of N. farcinica were divided into three groups, and the type strain was in group C-53. On the other hand, the strains of N. nova differed distinctly from the other two species and belonged mainly to groups C-56 and C-57. Our detailed analysis of mycolic acids was simple and precise. Therefore, the use of this method should be encouraged more for nocardial classification in combination with DNA or RNA analysis.