The "Reversal," Neutralization, and Selectivity of Germicidal Cationic Detergents.

The reversal of the inhibitory action of antiseptics by substances showing a specific affinity for the inhibiting agent has been reported for many compounds, the most striking effect probably being the reversal of the action of mercurials by H2S, glutathione, sodium thioglycolate, etc. Valko and DuBois (1944) have reported that the germicidal action of cationic detergents against both gram-positive and gram-negative bacteria can be reversed by the anionic detergent duponol PC (sodium lauryl sulfate). In the present work we have studied the ability of anionic detergents to reverse or neutralize the action of cationic detergents. We have found that anionic detergents did not reverse the germicidal action of cationic detergents against either gram-positive or gram-negative bacteria. If the cationic detergent inactivated the bacteria, the addition of an anionic detergent did not result in any reactivation. However, when the anionic detergent was added before all the bacteria in a given inoculum were inactivated by the cation, the anionic detergent could neutralize the action of the cation against gram-negative bacteria and prevent any further germicidal action on the surviving bacteria. Against gram-positive bacteria the bacteriostatic action of the cationic detergent was not neutralized by an anionic detergent even though the anion was added before the cation. The failure to neutralize the action of a cationic detergent against gram-positive bacteria was found to be related to the high degree of selectivity shown by the compound for gram-positive bacteria.