Chapter 7.3 : Solid Media for Isolation

Abstract:

Both liquid and solid media are recommended for optimal recovery of mycobacteria. The advantage of solid media (tubed or in plates) is that they enable detection of mixed cultures and contaminants. Egg-based and agar-based media may be used. The main advantage of an egg-based medium is that it supports the growth of most mycobacteria and permits niacin testing. However, contamination occurs more easily involving the total surface of the medium. The main advantages of agar-based media are less contamination and earlier and easier visibility of colonial morphology. Colonial morphology aids in the identification of mycobacteria. Use of both nonselective and selective media is needed for isolation, the latter containing one or more antimicrobial agents to prevent overgrowth by contaminating bacteria or fungi ( 2 ).