Effects of polyene antibiotics on growth and sterol-induction of oospore formation by Pythium periplocum.

The effect of polyene antibiotics upon growth and sterol-induction of oospore production by Pythium periplocum was studied. Filipin and fungichromin markedly inhibited growth and prevented reproduction. Amphotericin B also prevented oospore production but only slightly inhibited growth. Pimaricin slightly inhibited growth and greatly decreased reproduction. Nystatin usually had no effect on growth and slightly stimulated reproduction. At 4 pg./ml., amphotericin B and fungichromin prevented oospore induction by 1 pg. cholesterol/ml. but had no effect on growth. Growth inhibition by amphotericin B and fungichromin was almost completely annulled by higher cholesterol concentrations, and prevention of oospore formation was partially annulled. These results generally support the hypothesis that polyene antibiotics act by interfering with the action of cellular sterols, but the growth inhibition which occurred on sterol-free medium suggests that a second mechanism may be operative.