The Action of Cationic Detergents on Bacteria and Bacterial Enzymes.

The bactericidal action of the quaternary ammonium detergents has not yet been satisfactorily explained. Recent reviewers (Putnam, 1948; Rahn and Van Eseltine, 1947; cf. Glassman, 1948) have not agreed that the amounts of these detergents lethal to bacteria are insufficient to cause any general denaturation of the bacterial proteins (Valko, 1946). Action by enzyme inactivation, either primary or secondary to some other injury, has been repeatedly suggested. Respiratory and glycolytic activity is depressed by detergents, and the inhibiting amounts were later shown to parallel roughly the lethal amounts (Baker et al., 1941a,b). However, the frequent survival of cells at concentrations of detergent which produced marked respiratory inhibition has cast doubt on an action by direct inhibition of enzymes. Hotchkiss (1946) demonstrated that nitrogen and phosphate compounds diffuse out of the cells with bactericidal amounts of detergents. As an alternative to the action by enzyme inhibition he suggested that the loss of substrates and cofactors by diffusion from the cytolyzed cells might account for the death of the cells and the observed metabolic inhibitions. We have investigated the problem because objections can be made to much of the earlier work. Confirmation is apparently required that bactericidal amounts of detergents are well below those amounts causing general protein denaturation. The fact that some enzymes survive treatment with a bactericidal agent (Rahn and Schroeder, 1941; Greig and Hoogerheide, 1941; Bucca, 1943) has sometimes been interpreted as evidence against action by specific enzyme inhibition. More important is the lack of precise correlations between the lethal and the metabolic inhibitory amounts of detergent. Hotchkiss and others (Glassman, 1948) have pointed out that these irregularities may all be attributed to the comparison of quantitative metabolic measurements with the essentially qualitative determinations of viability by subculture. If cell death and metabolic inhibition are demonstrated to occur together with the same amount of detergent, an investigation limited to intact cells still leaves one unable to decide which of the results is cause and which effect (Roberts and Rahn, 1946). This decision would be simplified if the sensitivity of the enzymes in question, in cell-free form, to the detergents at the bactericidal levels was known.