Inhibiting Effects of Lipoids upon Actions of Antiseptics.

Although many experiments have been performed which have shown that the antiseptics have a weaker action in blood serum and tissue juice than in water salt solution or bouillon, this diminution of action has always been ascribed to the presence of the proteins. However, since these fluids also contain lipoids, and since, as has been shown by Cruikshank, 1 Loewe 2 and others, the lipoids may play a decided rôle in altering the distribution coefficient of the antiseptic dyes, we have studied the effects of the mere presence of lipoids upon the action of various antiseptics. In the experiments which we have performed, we have found that when cultures of Staphylococcus aureus and Bacillus coli are exposed to the action of various antiseptics (acriflavine, pyridium, phenol, bichloride of mercury) in suspensions of 0.5% lecithin or kephalin, or of .05% cholesterol, the antiseptic activity was greatly weakened; and this decrease of effectiveness is of about a degree similar to that which is brought about by the presence of an equal concentration of protein, though usually somewhat less marked. Since blood plasma contains .25% lecithin and .18% cholesterol, suspensions which we have used are quite comparable to blood plasma.

The table below gives the greatest dilution in Clark's buffer solutions (Na₂HPO₄+KH₂PO₄ at pH 7.4) of the antiseptics which inhibited the growth of transplants to agar after the bacteria have been exposed to the action of the antiseptic for 3 hours. The experiments with pyridium were done in Locke's solution as the antiseptic is precipitated by the phosphate buffer at pH 7.4.

Longer exposure to these antiseptics gave commensurate results except in the case of acriflavine and cholesterol, in which the control showed no growth in 1:54,000 after 12 hours and 1:500,000 after 24 hours, while in the presence of .05% cholesterol, inhibition occurred in 1:16,000 after 12 hours, and in 1:100,000 after 24 hours.

These results were obtained even in the absence of any visible flocculation of the lipoid suspension.

We have also observed with the ultramicroscope the effect of antiseptic on lipoid emulsions. The quinine series give blue or greenish Tyndall cones, though no particles can be seen. Lecithin emulsion shows large slowly moving particles. With addition of quinine, for instance, the particles may be seen to form large clumps, and clots are formed, while the blue Tyndall cone becomes weaker, and if sufficient lecithin is added, disappears. Similar results are obtained with the yellow cone of acriflavine.