The selective bacteriostatic activity of sulfanilic acid

Abstract

In a recent communication to this Society report was made of a selective bacteriostatic property exhibited by acid fuchsin. From a study of the effect of this dye on spore-bearing gram-positive aërobes and on the commoner gram-negative bacteria its selective activity was shown to be just the reverse of that exhibited by gentian violet and the other basic tri-phenyl-methane dyes: the latter kill the gram-positive aërobes and spare gram-negative bacteria, while acid fuchsin kills the gram-negatives and spares the gram-positive aërobes.

Magenta is one of the basic tri-phenyl-methanes and has the same effect on bacteria as gentian violet. From magenta, acid fuchsin differs only (so far as chemical structure is concerned) by the presence in its molecule of sulphonic-acid groups. Since the two dyes are—with this exception—identical, and since they have—so far as gram-positive aërobes and the commoner gram-negative bacteria are concerned—exactly opposite effects, it was clearly indicated to determine whether the sulfonic acid groups in acid fuchsin were responsible for its ability to kill gram-negative organisms while sparing gram-positive aërobes.

The behavior of sulfonic acid groups was tested by a study of sulfanilic acid. It was found that this substance behaves exactly like acid fuchsin: the commoner gram-negative bacteria, when exposed to it at 45° C. are readily killed, gram-positive aerobes under the same treatment remaining uninjured. This would seem to be proof that the reverse selective property of acid fuchsin (reverse, that is to say, as compared with gentian violet) depends on the sulfonic-acid groups which it contains.

Since opposite selective activities have thus been demonstrated for two dyes (magenta and acid fuchsin)-one of which kills gram-positive spore bearers and spares gram-negatives, while the other does just the reverseand since the chemical group in the latter substance which is responsible for its selective activity has been determined, data would seem to be at hand for the determination of the fundamental cause of the difference between these two types of organisms.