Inhibitory Action of Lactic Acid on Certain Bacteria and Fungi

Abstract

In his instructions for the cultivation of fungi and especially the isolation of pure strains, Duggar1 recommends the use of lactic acid in the culture mediums. He claims that, in general, 0.5% of lactic acid is sufficient to prevent the growth of contaminating bacteria. As there is little or no available information concerning the inhibitory effects of lactic acid on any great variety of bacteria, although there is as to a few special forms, this work was undertaken with a view of determining the effect on common bacteria and certain fungi. Apart from its bearing on methods of cultivation, there is possibly a more important relation between bacteria and lactic acid. Under pathologic conditions lactic acid is the most widely distributed and abundant acid in the body. It is found in the tissues, in the secretions of the stomach, in abscesses, and in various fluids of the body. It is asserted by Fischer that an increased production of acids in the tissues is responsible, to a large degree, for the occurrence of edema. Therefore, since lactic acid is so commonly found in the body, it would seem that the action of this acid on bacteria might be a truer test of the tolerance of bacteria toward acid, that is toward the effect of the hydrogen-ion, than would be that of an inorganic acid like hydrochloric, as we are more nearly approximating common pathologic conditions found in the body. The method employed in these preliminary experiments was as follows :