The Inhibitory Action of Saliva on the Diphtheria Bacillus: The Antibiotic Effect of Salivary Streptococci

Abstract

This report is concerned with the inhibitory action of saliva on Corynebacterium diphtheriae; the role of salivary streptococci in this inhibition and with several factors which influence it. The method used involved dropping standard drops of the material to be tested onto pour plates containing suitable dilutions of bacilli and observation of the zones of inhibited growth around the drops. Pure cultures of "mitis" type Viridans streptococci isolated from saliva inhibited the growth of the bacilli in the same manner as did fresh saliva. Removal of the streptococci from saliva by centrifugation, heat, or by the bactericidal effect of copper, abolished the inhibitory power. The actions of saliva and of pure cultures of streptococci were affected in identical fashion by several factors. Both actions were best demonstrated when the tryptose content of the medium was between 0.2% and 0.5% and were completely abolished on medium containing 2% tryptose. Both actions were antagonized by certain organisms present in saliva, especially staphylococci. The actions of both saliva and cultures of streptococci were increased by their suspension in nutrient media rather than in saline. The increased activity was associated with increased growth of the streptococci. The inhibitory action of saliva was destroyed by 56 [degree]C in approx. the same time as was the action of pure cultures of streptococci. The destruction paralleled the diminution in numbers of streptococci. It is concluded that the inhibitory action of saliva against C. diphtheriae demonstrated by the method used is due to the inhibitory streptococci present in the saliva.