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Chapter 7.3 : Solid Media Used for Isolation
Both liquid and solid media are recommended for optimal recovery of mycobacteria. Pure cultures of mycobacteria, particularly Mycobacterium tuberculosis, are still required, despite molecular technology, to obtain antimicrobial susceptibility test results and for strain subtyping. The advantage of solid media (tubed or in plates) is that they enable the 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 best supports the growth of M. tuberculosis and permits niacin testing. However, contamination occurs more easily and can involve the total surface of the medium. The advantages of agar-based media include less contamination and ear lier and easier visibility of colonial morphology. Colonial morphology aids in the identification of mycobacteria. Use of both nonselective and selective media is needed for optimal mycobacterial isolation, the latter containing one or more antimicrobial agents to prevent overgrowth by contaminating bacteria or fungi ( 1 , 2 , 3 , 4 ).