The Adsorption of Cetyltrimethylammonium Bromide by Bacteria, its Action in Releasing Cellular Constituents and its Bactericidal Effects

SUMMARY: The form of the uptake curve of cetyltrimethylammonium bromide (CTAB) by Staphylococcus aureus and Escherichia coli is that of an adsorption isotherm. Tested on six different bacteria, the maximum amounts of CTAB adsorbed showed variations from one organism to another. When cells of Staphylococcus aureus, Streptococcus faecalis, Escherichia coli or Salmonella pullorum are suspended in water, the ultra-violet spectrum of the super- natant liquid has a maximum absorption at a wave-length of 260 mp. The height of this maximum is greatly increased when the cells are suspended in CTAB solutions instead of water. Free purines and pyrimidines contribute to this maximum. There is a parallel relationship between the leakage of 260 mp.-absorbing material, glutamic acid and inorganic phosphorus from two CTAB-treated Gram-positive bacteria, when their release is followed during the initial rapid phase of leakage. There is a similar relationship for Esch. coli, although no glutamic acid is released. Release of cell constituents from CTAB-treated Staph. aureus continues slowly for some time after the initial process and is accompanied by a decrease in dry weight of the cells and a gradual change from positive to negative in their Gram-staining reaction. The rate of release' of cellular constituents was increased by raising the temperature or by treatment with high concentrations of CTAB. Treatment of suspensions with sufficient CTAB to sterilize them released amounts of cell constituents comparable to those released by placing the cells in boiling water. When smaller amounts of CTAB were used, a quantitative relationship was found between the amount of CTAB present, the proportion of cells killed and the amount of 260 mp.-absorbing material released. Many surface-active agents are bactericidal and various explanations have been proposed to account for this action. Baker, Harrison & Miller (1941) suggested that detergents disorganize the cell membrane and denature certain proteins essential to metabolism and growth. Kuhn & Bielig (1940) observed that germicidal concentrations of some detergents correspond to concentrations effecting denaturation of proteins. Hotchkiss ( 1944, 1946) found that treat- ment of bacterial cells with certain surface-active compounds in bactericidal concentrations released nitrogenous and phosphorus-containing substances. Gale & Taylor (I 947) demonstrated that the nitrogenous substances released included the free amino-acids concentrated within the cells of Strep. faecalis ; Mitchell & Crowe (1947) showed that this action was accompanied by an alteration in the surface structure of the cells, as shown by the electron microscope. By growing Staph. aureus and Pseudornonas jluorescens on media containing radioactive phosphorus (P37, Salton (1950) showed that there was an increased leakage of P32 into the suspending fluid when CTAB was present. The release of purines and pyrimidines from Staph. aureus treated with CTAB was reported by Salton & Alexander (1950).