Production of L-forms of Streptococcus pyogenes and their antitumor effects.

Unstable L-forms of Streptococcus pyogenes were effectively isolated when protoplasts induced by muralysin were cultivated on a gradient plate containing penicillin-G. By this method, L-forms were obtained from the strains of serotype 3 and 4, from which they had been considered to be difficult to obtain. After 30 to 40 subcultures, two L-form strains (L-forms of Su and C-512) were successfully transferred into fluid medium without serum and penicillin. The antitumor effects of these stable L-forms were compared with these parent cocci. Treatment of the L-form of Su, which has antitumor effect, showed a considerable prolongation of life span in mice inoculated with Meth-A ascites tumor. On the other hand, the L-form of C-512, which has no antitumor effect, produced no effect on the tumor growth. Using two different transplantable tumors, the antitumor properties of th L-form of Su were investigated by comparing them with protoplast and cell wall fraction derived from the Su strain. In ascites tumors, the L-form treatment showed visible effects, while the cell wall produced no inhibitory effect. On the contrary, in solid tumors the antitumor effects obtained by the administration of the cell wall were never improved by the L-form. In both types of tumor, L-form showed antitumor activities similar to protoplast.