Inhibiting Effect of Acetic Acid upon Microorganisms in the Presence of Sodium Chloride and Sucrose

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Abstract
Acetic acid inhibited bacterial growth in almost direct proportion to the amt. present. The order of decreasing resistance to acetic acid, either alone, in 5% brine or in 20% syrup was Bacillus cereus, Salmonella aertrycke, Staphylococcus aureus, and Phytomonas phaseoli. Naturally, Saccharomyces cereviseae and Aspergillus niger were inhibited at a higher acetic acid conc. than the bacteria, with the yeast being the more resistant. A. niger was grown in flasks of 0.5% glucose broth containing acetic acid, acetic acid and salt, and acetic acid and sugar. Dry weights of the molds from various flasks were compared. In all cases the mold was inhibited at pH 4.1 and at a total acidity of 0.27%. At equivalent total acidities the pH values of the acidified distilled water were slightly lower, in general, than those of the acidified syrups and slightly higher than those of the salt brines of corresponding total acidities. At equivalent pH values greater toxicity was usually observed in those tubes containing the greater amt. of acid. Apart from the indirect effect in altering the pH, 5% NaCl and 20% sucrose increased only slightly the toxic effect of acetic acid to bacteria and yeast. The presence of acetic acid in an amt. which neither prevented nor inhibited mold growth actually promoted development of A. niger by acting as a source of energy. Also in nontoxic nutrient solns. the mold utilized the sugar to produce a more luxurious growth than when grown in either plain 0.5% glucose broth or in this broth containing 5% NaCl. Additional evidence is presented to show that the toxic action of acetic acid to microorganisms is not confined to the pH.