Antibiotic inhibition and binding studies with a group A streptococcal L-form.

The minimal inhibitory concentrations of various antibiotics for a strain of Streptococcus pyogenes and a stable L-form of it were determined. These results were evaluated with those of other investigators similarly performed with S. faecalis and derived protoplasts. Differences in reaction to puromycin, bacitracin and ristocetin were apparent only between the wall-less derivatives. The polyene antibiotics nystatin and filipin and two antimicrobial agents, isatin 3-thiosemicarbazone and 1-methyl-isatin 3-thiosemicarbazone, were ineffective or only slightly inhibitory on growth of S. pyogenes and its L-form. Labelled penicillin studies with this group A streptococcus and its L-form indicated that the binding sites for penicillin were probably distinct from those concerned with streptococcal wall formation.