A considerable amount of work has been reported on the surface-active cations, and several workers have shown that, although these compounds are highly germicidal, they are also highly bacteriostatic in relatively high dilutions. Although these compounds are highly bacteriostatic, there has been little work done to distinguish between actual germicidal activity and bacteriostatic action. Baker, Harrison, and Miller (1941) made the first attempt to separate bacteriostatic from germicidal action

more »

... y the use of phospholipids. They found that the effect of the cationic compounds upon the test bacteria was seriously impaired when the bacteria were added simultaneously with the phospholipids. They were, however, unable to revive the bacteria once they had been in contact with the cationic compound. Valko and DuBois (1944) were the first workers to show the so-called reversibility of the surface-active cations. They were able by the use of "duponol PC" to neutralize in part the effect of a 1:3,000 dilution of "zephiran" upon Staphylococcus aureus after 10 minutes' exposure. Using Escherichia coli and Eberthella typhosa, they were able to obtain reversal up to 5 minutes. The measurement that they used for kill or survival was the absence or presence of growth in the broth subculture tubes. As mentioned by Hotchkiss (1946) this is a qualitative rather than a quantitative procedure and assumes either complete killing or no killing at all rather than the percentage surviving. Unfortunately, although such data show that neutralization has occurred, there is no information upon the degree of neutralization. The work presented in this paper further substantiates the fact that the action of the surface-active cations is reversible. The techniques used vary from those of previous workers in the method of approach and in that they are quantitative. EXPERIMENTAL METHODS AND RESULTS These studies were initiated originally by the fact that when spores of Bacillus subtilis were exposed to surface-active cations, complete killing was obtained after short periods of exposure. The writers were firmly convinced that the bacterial spores were not susceptible to this degree to the action of these compounds and that the apparent killing was actually a bacteriostatic action. When the treated spores were subsequently treated with anionic neutralizing agents, a few spores recovered from their inhibition, but the apparent percentage of killing was still exceedingly high. It was finally decided to attempt the removal of the excess surface-active agent by centrifugation of the treated spores followed by repeated washing with sterile distilled water or physiological saline. This procedure gave 565 on May 9, 2020 by guest