The phage tellurite zonal phenomenon as a criterion for the differentiation of slowly growing Mycobacteria.

Formerly, only Mycobacterium tuberculosis, Myco. bovis and Myco. avium were recognized as the main acid-fast micro-organisms responsible for producing delayed-type sensitivity to tuberculoproteins and for causing tuberculosis.Recently, many other slowly growing acid-fast micro-organisms have been isolated and recognized as potential human pathogens. The differentiation of these strains is much more difficult than that of the "typical" ones, however, and calls for new techniques. One such technique is the phage-typing of mycobacteria. Phage studies have revealed a hitherto unknown phenomenon-namely, that the lytic plaques produced by phages on slowly growing mycobacteria (whether sensitive or resistant to the major antituberculosis drugs) display, at the boundary with the non-lysed culture, a zone of irregular width formed by mycobacteria that have lost their ability to reduce potassium tellurite to metallic tellurium. By contrast, the lytic plaques produced by phages on rapidly growing mycobacteria with strong tellurite reactivity always display a sharp line of demarcation between the plaque and the non-lysed culture.The studies described in the present paper have shown that the tellurite zonal phenomenon provides a reliable criterion for the differentiation of slowly growing mycobacteria.