VARIATION OF M-PROTEIN WITH SEQUENTIAL TRANSFER OF GROUP-A STREPTOCOCCI IN SEMISYNTHETIC MEDIA

Abstract

The growth and production of M protein [which is the group A streptococcal virulence factor] by 18 strains of Streptococcus pyogenes of different M types were compared in semisynthetic media having starch or Tween 80 as binders of oleic acid and acid-hydrolyzed casein or casitone as a source of amino acids. Most strains of M-type 12 showed substantial loss of M protein synthesis within several sequential transfers in the casein hydrolysate-Tween (CH-Tw) medium, but M protein synthesis was brought to its original concentration by a single transfer to semisynthetic medium to which 4% (vol/vol) horse serum or 50% (vol/vol) Todd Hewitt broth were added. Six of 8 strains of M-type 22 showed a complete loss of M antigen within 1 or 2 transfer in the CH-Tw medium. Re-initiation of M protein synthesis required the presence of both Todd Hewitt broth and horse serum. No evidence was found correlating loss of M protein to synthesis of proteinase, since proteinase was not formed in the CH-Tw medium. Although the genetic loss of M protein synthesis did occur with 1 strain, the experimental results emphasized that variation in specific concentration of M protein or cessation of its synthesis resulted primarily from the absence of nutritional factors regulating its synthesis.