Osmotic fragility of the group A streptococcal L form

The osmotic fragility, expressed in terms of survival, of two group A streptococcal L-form strains was examined by suspending the L form in sodium chloride and sucrose solutions of graded concentrations. An immediate and marked reduction in viability followed suspension in sodium chloride solutions of less than 0.7m. A wide distribution of osmotic fragility within the L-form population was observed. The two L-form strains (GL-8 and AED) differed in that the AED L-form strain appeared to be consistently more resistant to osmotic lysis, and survived considerably better in sodium chloride solutions up to 90 minutes. Sucrose solutions of tonicities comparable to those of the sodium chloride solutions used, however, stabilized the labile GL-8 L form completely. Magnesium chloride (0.05m) and serum (10% v/v) substantially increased L-form survival in sodium chloride. The results are interpreted to indicate a difference in the cell envelope of the two L-form strains, the AED limiting membrane possessing a greater intrinsic stability. The significantly greater resistance to sonic oscillation of the AED L form as compared to the GL-8 L form, is in agreement with and supports this conclusion. The possibility that the difference in physical properties of the two L-form strains is related to a difference in chemical composition of their limiting envelopes is discussed.The author wishes to thank Dr. W. Hijmans for his interest and advice, and Miss H. L. Ensering and Miss M. J. W. Kastelein for technical assistance.