The inhibitory action of fatty acids on the growth of Escherichia coli.

The effect of fatty acids on Escherichia coli K12 was dependent on the source of the inoculum, the growth phase and the washing of the bacteria. The effects of saturated fatty acids from C4 to C16 and oleic acid at two concentrations (0-I and 0-4%, w/v) were determined on E. coli K12/154 growing exponentially in five different culture media. Depending on the media, 0-I % fatty acids increased the doubling times of the cultures by up to 96 %. Fatty acids of medium chain length (C6 to CII) at 0-4 % produced a decrease in cell concentration, nonanoic and decanoic acids being the most effective. A correlation was found between the decrease in cell concentration and the loss of viability of the culutres after addition of 0-4 % decanoic acid, with stationary-phase bacteria being affected more than those from exponential-phase cultures. Experiments carried out with E. coli B and C gave results similar to those obtained with E. coli K12/154.