Size Determination by Phase-contrast Microscopy of the Reproductive Elements of Group A Streptococcal L-Forms

SUMMARY Slide cultures consisting of small agar blocks were inoculated with the L-forms of two group A streptococci strains GL-8 and AED grown in broth. The size of the L-form elements was measured on photographs taken immediately after inoculation of the slide cultures. The diameter of the elements varied between 0-2 and 3.0,~. The frequency distribution of the diameters has a bimodal form. This bimodality probably represents the size distribution of two classes of L-form elements which can arbitrarily be divided at the diameter of 0.7 p. The reproductive elements of the streptococcal L-forms were found, with a few exceptions, to have a minimal diameter of 0.7 p (average diameter 1-4 and 1.2 p, respectively; standard deviation 0.3 p). Slide culture experiments with concentrated filtrates of 0.45 filters showed that the reproductive elements present in the filtrates ranged in size from 0.8 to I -7 ,u with an average diameter of I -2 ,u (standard deviation 0.2 p). The filterability of the streptococcal L-form might therefore be mainly due to the plasticity of the L-form elements.