The Bacteriostatic Action of Phenol, Benzoic Acid and Related Compounds on Bacterium aerogenes

SUMMARY: A method was developed that permitted the immediate and relatively uncomplicated study of the inhibition of Bacterium aerogenes during the logarithmic growth phase. With the ten aromatic compounds tested the linear growth rate was immediately established in the presence, as well as in the absence, of inhibitor.

The results with Bact. aerogenes, as well as some similar determinations with Aspergillus niger, using 50% inhibition as criterion, suggest that in the phenols and in the acids, considered separately, there is a reasonably inverse relationship between inhibiting potency and water solubility. Substitutions that lead to an ortho-relation-ship between hydroxyl and carboxyl groups do not lessen but rather increase potency; meta- and para-substitutions of these groups lessen potency.

On the hypothesis that inhibition is proportional to the number of inhibitor molecules adsorbed at the surface of a susceptible metabolic system, potency can be analysed in terms of two factors: (a) the ability to adsorb on such a surface, which largely parallels 50% inhibition; and (b) the degree of saturation of the surface with increasing inhibition, which is small for the phenols, large for the benzoic and the two dihydroxybenzoic acids, and intermediate for the monohydroxybenzoic acids.