Phage typing of the Mycobacterium avium-intracellulare-scrofulaceum complex

Because of the need for additional criteria for characterizing strains of the M. avium-intracellulare-scrofulaceum (MAIS) complex the practicality of phage typing was examined. We developed a satisfactory method for plaque assays with these organisms using the soft-agar overlay technique with Dubos oleic acid-albumen agar. Cells were cultured in 7H9 broth enriched with oleic acid-albumen complex and glycerol. A number of available phages and 2 phages recently isolated from soil were tested for their ability to infect various MAIS strains. Phages AN9, AN3, AN1-8, D302, VA6, VC3, D32, JF1, JF2, JF3, and JF4 were selected for preliminary typing. All of the phages were propagated on M. smegmatis. Sixty-one MAIS strains having 29 different serotypes were tested and 33 were sensitive to at least 1 phage. Of 17 M. avium strains (serotypes 1, 2, and 3), 16 were phage-sensitive. Considerable diversity in patterns of phage lysis was observed, and the patterns of lysis did not coincide with serotype. Although we do not yet have a formal phage typing scheme, our results indicated that the MAIS strains are suitable for phage typing.