Relation of pH to Preservative Effectiveness II

Liquid trypticase soy broth media was buffered with Prideaux and Ward's universal buffer to neutral and basic pH levels (pH 7 to 10 inclusive). Preservative solutions of various concentrations were added to tubes containing the media, After inoculation of the tubes with a slurry obtained from soil samples suspended in water, these preparations were examined for preservative effectiveness over a 6-month period. In most cases preservative effectiveness varied with pH alteration. The preservative activity ranged from negligible with cinnamic acid and some of its derivatives, the amides of bromal and dichloroacetaldehyde, sorbic acid and dehydroacetic acid-sodium, to fair in the case of parabens and salicylanilide, to good with cetrimide, chlorophenesin, vanillic acid esters, hexylresorcinol, hexachlorophene, and phenylethanol.