[Selection of phage-resistent clones of streptococcus group A and their properties]

In studying the effects induced by virulent phage CAI in the sensitive cultures of streptococcus, group A, a possibility was shown of selection of phage-resistant clones with the altered enzymatic activity. These clones lost their capacity to produce proteinase and retained residual lipoproteinase activity. This evidence correlates with literature data indicating that phage-resistant streptococci served as good producers of M-protein--the main virulence factor. Infection of the culture producing streptokinase with phage CAI with a definite infection multiplicity led to an increase of the enzyme activity in the culture fluid. This process was accompanied by selection of the resistant strains characterized by greater streptokinase production and greater enzyme stability. As suggested, the latter could result from the absence of proteolytic activity in the phage-resistant clone.