The initial structural lesion of penicillin action in Bacillus megaterium.

The effect of penicillin on the structure of Bacillus megaterium cells was followed in media with and without osmotic stabilization. In peptone without osmotic support the cells showed a distortion of the normal membrane-wall relationship by 20 minutes. This appeared to be a combination of both membrane distortion and cytoplasmic leakage. Lytic changes quickly followed. With osmotic support a clean-cut lesion at the transverse-septal site developed by 10 minutes' growth in penicillin. The membrane lost its normal relationship to the cell wall and formed a pocket which was filled with a fibrous material which appeared to be unorganized wall mucopeptide. The pocket of fibers enlarged until the cell either lysed or formed a protoplast.