Evaluation of defined media suitable for isolation of auxotrophic mutants of mycobacteria.

In order to investigate the production of auxotrophs of slow growing mycobacterial pathogens, an evaluation of defined liquid and solid media suitable for Mycobacterium tuberculosis, Mycobacterium bovis and Mycobacterium paratuberculosis was undertaken. Five defined liquid media were evaluated. A number of solid support matrices was added to the liquid media to produce solid media for evaluation. Tween 80 was added to all media to produce diffuse homogeneous growth. Although satisfactory growth in defined liquid media was achieved with all strains tested, poor growth was generally observed in the equivalent defined solid medium for strains belonging to the tuberculosis complex. Only M. paratuberculosis produced satisfactory growth on defined solid media, especially on Middlebrook 7H9. The inhibitory effect of Tween 80 and the presence of inhibitory factor(s) in agar were confirmed. Partial removal or inactivation of these factors by the addition of absorbents to the media was achieved.