A New Antibacterial Principle: Megacine

Abstract

IN the course of an investigation of the potential lysogenic powers of B. megaterium strains isolated recently from fæcal and soil samples, one of the strains studied (No. 216) showed a particular effect. When a highly diluted broth culture of this strain was mixed with a heavy suspension of a phagesensitive B. megaterium strain (‘mutilate’), and plated on yeast extract agar containing casein hydrolysate, no phage plaques were seen, but the colonies of the strain 216 were surrounded by a small clear halo. To study this effect, young aerated cultures of the strain grown in yeast extract–casein hydrolysate broth were lightly irradiated with ultra-violet light and reincubated. The turbidity of these cultures increased after irradiation up to the end of the second hour; then a lysis of the bacteria set in, which became almost complete in three hours. The bacterial lysate thus obtained does not contain phage particles when tested in the usual way. On the other hand, if one drop of various dilutions (up to a few thousands) of the lysate was put on the surface of a yeast extract–casein hydrolysate agar plate heavily seeded with B. megaterium, it caused a clear spot with no bacterial growth on the site of the drops. There was no reproduction of the antibacterial principle (which we propose to call ‘megacine’) in the sensitive bacteria, which fact excludes its phage character.