Use of selected ion monitoring for detection of tuberculostearic and C32 mycocerosic acid in mycobacteria and in five-day-old cultures of sputum specimens from patients with pulmonary tuberculosis.

Gas chromatography/mass spectrometry and selected ion monitoring (SIM), employing both electron (EI) and chemical ionization (CI), was used to detect 10-methyloctadecanoic (tuberculostearic) and 2, 4, 8, 8-tetramethyloctacosanoic (C32 mycocerosic) acids in bacteria of 14 species of Mycobacterium and 3 species of Nocardia. Tuberculostearic acid was found in all species studied, while C32 mycocerosic acid was demonstrated only in M. africanum, M bovis, M. bovis strain BCG, M. kansasii and M. tuberculosis. The relative amounts of these acids in the organisms of these five species varied, thereby constituting a presumptive diagnostic technique. The lowest detectable amount of C32 mycocerosic acid was approximately 5 pg when using EI-SIM, monitoring at m/zz 88 and m/z 101. When using CI, employing isobutane as reactant gas, and focusing at m/z 495, 2 pg could be detected, and when ammonia was the reactant gas, the corresponding figure was 1 pg, monitoring at m/z 512. Tuberculostearic acid was demonstrated in 5-day incubated sputum specimens from 6 patients with pulmonary tuberculosis, including 5 patients infected with M tuberculosis and 1 patient infected with M. avium. C32 mycocerosic acid was detected in 4 of the 5 patients with M. tuberculosis infection. None of the acids was found in a further 8 patients who had viral or bacterial (non-mycobacterial) pneumonia. Tuberculostearic acid could be demonstrated in 10 of another 12 sputum specimens from patients with tuberculosis, when the samples were analyzed directly, viz prior to culturing. The possibility of using SIM for the rapid diagnosis of pulmonary tuberculosis is thus worth consideration.