EFFECTS OF COMMON BACTERICIDAL SUBSTANCES AND OF HEAT ON YEAST GROWTH AND VIABILITY

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Abstract
Investigating the effects of a number of common inorganic and organic bactericidal substances upon the viability and growth of a strain of baker's yeast, three criteria of toxicity towards yeast have been examined: the killing powers of these substances on aqueous yeast suspensions; the inhibitory action of the substances towards yeast growth in aerated liquid media; and inhibition of yeast development on agar plates of defined composition. The toxicity of chemical substances is shown to vary considerably with the nature of the test employed, but two quaternary ammonium compounds showed high toxicity whatever test was used. Small numbers of yeast cells exhibit considerably greater resistance towards the action of heat and bactericidal substances than do the bulk of the yeast cells of any yeast sample. Apart from this “population effect,” no common law could be found governing the rate of cell destruction in these tests in which the law of exponential decline was found inapplicable.

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