Identification of Clinical Isolates of Mycobacteria with Gas-Liquid Chromatography Alone

Abstract

Identification of 18 mycobacterial species was performed by analysis of profiles obtained by using GLC. Organisms were saponified in methanolic NaOH and the reaction mixture was treated with BF3 in methanol and extracted with a hexane-chloroform mixture. An identification scheme was developed from 128 stock strains and tested against a collection of 79 clinical isolates. By using GLC profiles alone, 58% of specimens were correctly identified to species level and an additional 41% were correctly identified to 2 or 3 organisms. Use in a clinical laboratory over 2 mo. proved GLC to be as accurate as and more rapid than concurrent biochemical testing. Of 81 isolates tested, 64% were identified to species level by GLC alone. An additional 35% were differentiated to the same groups of 2 or 3 organisms as found in the analysis of stock strains. These groups consisted of: Mycobacterium tuberculosis, M. bovis and M. xenopi; M. avium complex, M. gastri and M. scrofulaceum; or M. fortuitum and M. chelonei. Identification to species level from these groups could usually be done by colonial morphology alone and could always be done by the addition of 1 selected biochemical test. This study demonstrated the practical application of GLC in the identification of mycobacteria in a clinical laboratory. In particular, all strains of M. gordonae and M. kansasii were identified to species level. M. tuberculosis was definitively identified in 85% of cases. When it could not be definitely identified, the only alternatives were M. bovis and M. xenopi, both rare causes of infection.