The selective bactericidal effect of acid fuchsin and sodium chloride

Abstract

In 1912 it was found that if bacteria be stained with gentian violet and planted on plain agar a sharp selective activity of the dye could be readily demonstrated. All the commoner gram-negative organisms survived even long exposure to the stain, while all the commoner gram-positive spore-bearing aërobes were “killed,” even by a relatively short exposure. Even the spores—though not deeply, if at all, stained by gentian violet—were “killed” by exposure to the dye. What was true of gentian violet was found to be true also of other basic dyes of the triphenyl-methane group.

It is now found that a cleavage in exactly the opposite sense occurs if organisms be exposed to acid fuchsin—an acid dye of the tri-phenyl-methane series. Whereas gentian violet kills the gram-positive spore-bearing aërobes and spares the commoner gram-negative bacteria, acid fuchsin spares the former and kills the latter. The experiments on which this statement is based were done with B. subtilis, B. megatherium, B. anthracis, B. typhosus, B. coli communis, B. prodigiosus, B. pyocyaneus, B. proteus vulgaris. In the case of gentian violet the reaction is evident if the stain is applied to the organisms at room temperature; but in the case of acid fuchsin, while long exposure to the dye at room temperature produces the reaction, a slight increase in temperature (to 45° C.) makes it much sharper and speedier.

In the case of gentian violet it was shown, by a study of the whole bacterial field, that the gentian-violet reaction and the gram reaction ran parallel in a striking way. Not only did the cleavage hold between gram-negative organisms and the commoner spore-bearing aerobes; it also held between gram-negative bacteria and the great majority of non-spore-bearing gram-positive organisms.