Accidental contamination of diagnostic cultures of mycobacteria and phage identification of the contaminating strain.

Phage typing of mycobacteria is a new technique not yet widely used for classification and intraspecies differentiation. Systematic long-term studies organized by the WHO have succeeded, using a battery of 11 different mycobacterial phages, in dividing M. tuberculosis into 3 different phage sub-groups, preliminarily labelled as A, B and C. A special case of phage-typing is presented which enabled identification of a virulent mycobacterial strain causing accidental contamination of diagnostic mycobacterial cultures. The strain was an old laboratory one, H37Rv, belonging to phage subgroup B.