Enhancement of growth of Mycobacterium malmoense by acidic pH and pyruvate

The growth of Mycobacterium malmoense is dysgonic and slow on ordinary mycobacterium media. The effect of pH and pyruvate on the growth of ten strains was studied on a modification of Löwenstein-Jensen medium. Growth appeared sooner and was more abundant at pH less than 6.5. At pH 7 or higher, it was scarcely or not at all visible after six weeks of incubation. Pyruvate enhanced the growth of five strains that grew only poorly on glycerol-containing medium, even at acidic pH. The parallel use of both pyruvate and glycerol-containing media, pH 6 to 6.5, and an incubation period of seven weeks or longer are recommended for the isolation of Mycobacterium malmoense on Löwenstein-Jensen medium.