Effect of Various Nonionic Surfactants on Growth of Escherichia coli

Abstract

Escherichia coli cultivated in media containing 0.5, 1.0, 2.0, or 4.0% concentrations of surface-active polyoxyethylene derivatives of formaldehyde polymers of octyl phenol (Triton WR-1339; Macrocyclon) or of sorbitan mono-fatty-acid esters (Tween-20, -40, -60, and -80) exhibited significantly retarded growth only at the highest concentration. To determine the mechanism of bacteriostasis, certain derivatives and compounds related to the surfactants were investigated. Experiments with compounds related to the Triton-type agents demonstrated that incorporation of monomeric substances (Triton X-205, X-305, Igepal CA-730, or Dowfax 9N20) into the medium at a concentration of 4.0% did not inhibit the growth of E. coli. It was concluded that the formaldehyde polymer was essential for growth inhibition by the polyoxyethylene derivatives of octyl phenol. The inhibitory activity of the Tween compounds, in contrast, appeared to result from the unesterified fatty-acids which contaminate the commercial preparations. Polyol (60), the sorbitan polyoxyethylene derivative of Tween-60 and the basic structural unit of all the Tween -type compounds, and a Tween-80 preparation which was purified by extraction of the unesterified oleic acid were not inhibitory. Moreover, the amount of free oleic acid present as a contaminant of Tween-80 was found to be sufficient to cause significant growth inhibition. These results and the observation that E. coli does not appear to hydrolyze the esterified fatty-acid of Tween-80 led to the conclusion that growth inhibition obtained with various Tween compounds probably is a func -tion of their respective fatty-acid contaminants.