The fungistatic properties of p‐aminobenzoic acid and related compounds. Part I. Growth curves obtained with aspergillus niger, penicillium roqueforti and byssochlamys fulva

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Abstract
A. niger, growing in the presence of p‐aminobenzoic acid and its lower alkyl esters, departs significantly from linearity in media of approximate pH 3 to 5, containing nitrate nitrogen. This effect is not observed where media are of pH 6 to 7 or nitrogen is supplied solely as the ammonium ion or the free para‐amino grouping is acetylated or with the corresponding ottho‐ or meta‐aminobenzoate. The non‐linear growth rates can be interpreted in terms of an initial phase, a phase of secondary inhibition and a period of outgrowth. Inhibition in the initial phase is appreciably less at higher pH levels.P. roqueforti growing in the presence of esters of p‐aminobenzoic acid in media where pH rises during growth shows an accelerating curve. This effect is associated with a marked loss of inhibitory power at pH greater than about 5·7. A similar acceleration is seen with methyl N‐acctyl‐p‐aminobenzeate but has not been found with methyl p‐hydroxybenzoate. None of the free aminobenzoic acids departs from the linear growth curve with this organism.B. fulva gives an acceleration in the presence of methyl p‐aminobenzoate under the same conditions of pH and nitrate nitrogen as cause secondary inhibition of A. niger. In contrast to the other two organisms the less acid media (pH 5 and 7) are relatively more inhibitory, this being associated with absence of acceleration such as is seen under the more acid conditions. The three aminobenzoic acids give linear growth curves.