THE CYTOPLASMIC MEMBRANE AS THE SITE OF THE ANTIMICROBIAL ACTION OF N-OCTYLETHANOLAMINE

On agar spread plates, N-octylethanolamine was biocidal at comparable minimum inhibitory concentration (MIC) values (3-4 mM) against Pseudom onas aeruginosa (two strains), Escherichia coli, Staphylococcus aureus , Bacillus subtilis, Candida tropicalis, and Acremonium sp. which had been grown on a number of different media. The inhibition was greater at higher pH values. In liquid culture, growth inhibition by 3 mM N-oc tylethanolamine was accompanied by cell lysis. Both effects could be p revented by the presence of 1 mM spermine or spermidine, but only in b acteria, and not at high pH values. These effects of the polyamines we re shown to be non-specific, being shared by other polycations and Mg2 + ions. N-Octylethanolamine at concentrations above its MIC caused tot al inhibition of the oxidation of 1 mM glucose by Ps. aeruginosa (CAS1 and PAO1), E. coli, or C. tropicalis, an effect that was partially re versible by Mg2+ ions. At concentrations below the MIG, there was litt le inhibition of glucose oxidation but a potent inhibition of the extr usion of ethidium bromide from intact cells of E. coli, suggesting tha t at such concentrations N-octylethanolamine is uncoupling oxidative p hosphorylation. The data presented confirm the view that the biocidal effects are due to action on the cytoplasmic membrane.