Specificity of purified protein derivative extracts from cultures of mycobacteria killed by phenol.

Purified protein derivative (PPD) extracts were prepared from Mycobacterium bovis, M tuberculosis, M kansasii, M marinum, M avium, M intracellulare, M gordonae and M fortuitum. The cultures were killed with phenol before extraction and were not subjected to heat. They were tested in guinea pigs sensitised with killed cultures of homologous or heterologous species of mycobacteria. The most specific extract was from M fortuitum. M bovis and M tuberculosis were closely related, with M bovis PPD the more specific of the two. A close relationship was shown between M scrofulaceum, M avium and M intracellulare.