ACTIVITY OF P-AMINOBENZOIC ACID COMPARED WITH OTHER ORGANIC-ACIDS AGAINST SELECTED BACTERIA

The antibacterial activity of p-aminobenzoic acid against Listeria mon ocytogenes, Salmonella enteritidis and Escherichia coli was compared w ith the activity of commonly used acidulants: formic, propionic, aceti c, lactic and citric acids. Viable count evaluations and MIC determina tions indicated that p-aminobenzoic acid caused greater inhibitory eff ects than the other organic acids. The activity of p-aminobenzoic acid on the growth of the test organisms at selected pH values indicated t hat p-aminobenzoic acid was more active at low pH than at high pH. Upt ake studies showed that the uptake of p-aminobenzoic acid by E. coli w as markedly decreased as the pH values increased. Electron micrographs of E. coli cells grown in the presence of p-aminobenzoic acid indicat e that p-aminobenzoic acid caused marked damage to the cell envelope. It is suggested that p-aminobenzoic acid has at least two mechanisms o f action: one mechanism in common with other organic acids and the oth er mechanism by interfering with the synthesis of the peptidoglycan la yer by an action on the dihydrofolate reductase enzyme.