Protection of Dry Bacteria by Fat Against Cationic Detergents

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Abstract
Quantitative measurements of adsorption of quaternary ammonium compounds were made by leaving the adsorbent in contact with the detergent solution for some time, centrifuging, and measuring the surface tension of the supernatant. Bentonite adsorbed very strongly, filterpaper and yeast cells less, but measurably. Miller et al. (B. A. 18: abstr. 4967. 1944) had observed that Zephiran, adsorbed on the hands, did not kill the bacteria of the skin, but made the hands aseptic. This was verified by drying bacteria on surfaces of fat or paraffine, and exposing them to a 1% Zephiran soln., 200 times the minimal lethal conc. Some bacteria were alive after 4 hrs. and sometimes even after 20 hrs., while those dried on gelatin were killed by 0.1% Zephiran in 1/2 hr. This is explained by assuming a molecular adsorption film on fat, with the harmless, organophilic radicals oriented towards the fat, and the toxic, hydrophilic, nitrogenous part of the molecule towards the aqueous soln. On gelatin surface, the orientation is opposite to that on the fat surface.

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