Growth-inhibitory Substances in Pneumococcus

In the study of bacterial symbiosis and antagonism, considerable interest has centered in the presence or absence of growth when organisms are reinoculated into filtrates of cultures of the same or different species. The nature of the substances which favor or inhibit the simultaneous or subsequent development of bacteria in the same nutritive medium has provoked much discussion and stimulated considerable research. The inhibitory influence which different microorganisms exert on one another has been ascribed, for the most part, to an altered and unfavorable reaction brought about in the substrate by growth, or to exhaustion of the medium by the dominant species, these two factors either singly or together resulting in autoinhibition or in the suppression of the more susceptible variety. In addition, it has been assumed that certain deleterious waste products accumulate as a result of bacterial metabolism which react unfavorably on subsequent growth, or even cause mutual inhibition of both the homologous and heterologous organisms.