Many papers on the induction of L-forms of group A streptococci have appeared since Sharp (8) reported it. Most of the studies, however, were on the media (l, 6, 8) and drugs (3-7) used for induction. No study of the correlation between serotype and L-form induction has been reported. In this paper the induction of L-forms from various serotypes of group A streptococci is reported.The serotypes used are shown in Table I. The 56 strains, which were isolated from patients with streptococcal infections and from healthy carriers, were typed with T-factor sera (9) prepared in our laboratory. All of them were preserved by freezing at -30 G in heart infusion broth containing one drop of horse blood. A subculture of each strain was grown overnight in brain heart infusion broth (BHI, Difco) and 0.1 ml of the thoroughly mixed culture was inoculated onto an agar plate consisting of BHI, 4% NaGI, 1.25% glycine, I % purified agar, and 10% inactivated horse serum, and a penicillin-G disk was placed on the center of the plate. The agar plates were incubated in a candle extinction jar at 37 G, and on the 7th day the plates were examined for the presence of L-colonies. Incubation was continued for an additional 7 days if growth did not occur. L-colonies which appeared in the inhibition zone around the penicillin disk were counted.Induction of L-forms from the strains of group A streptococci of various serotypes and the number of L-colonies produced by the induction positive strains are shown in Table I. L-forms were induced from all strains of types 14, 25, 28, and Imp 19, and were from three of the 4 strains each of types I, 22, and B3264, whereas none of the strains of types 3 or 4 were induced.Some of the strains of the induced L-forms were transferred to and maintained on an agar medium prepared from BHI containing 4% NaGI, 1% agar, 1,000 units of penicillin-G per ml and 10% serum. The colonies of L-forms were transferred in the following way: a small block of agar containing L-colonies was excised and placed face-downward on the surface of a new agar plate and incubated at 37 G for 7 days, then the agar block was gently slipped onto the agar plate and incubated for an additional 7 days.The transferability of the 15 strains of induced L-forms was determined by using the agar medium described above. All of them were able to be transferred through the third generation; no further transfer was attempted.
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