169 Susceptibility of several species of gram-negative and gram-positive bacteria to organic acids and their derivatives

Abstract The objective of this experiment was to determine the in vitro antimicrobial activity of several organic acids and their derivatives against gram-positive (G+) and gram-negative (G-) bacteria. Monopropionin, monovalerin, monolaurin, and sodium formate were tested at 10 to 12 concentrations from 0.001 to 2.50 mg/L; monobutyrin was tested at 16 concentrations from 0.001 to 5.00 mg/L; butyric acid and valeric acid were tested at 8 concentrations from 0.001 to 0.35 mg/L; while formic acid was tested at 8 concentrations from 0.001 to 1.00 mg/L. The tested bacteria included G- bacteria (Escherichia coli, Salmonella typhimurium, and Campylobacter jejuni) and G+ bacteria (Enterococcus faecalis, Clostridia perfringens, Streptococcus pneumonia, and Streptococcus suis). Antimicrobial activity of tested compounds was expressed as minimum inhibitory concentration (MIC) that prevented growth of tested bacteria in treated culture broth. Butyric acid, valeric acid, and formic acid at highest tested concentrations inhibited the growth of all bacterial strains. The MICs of the three acids varied among bacterial strains with lowest MIC of 0.05–0.10 mg/L on two strains of Campylobacter. Sodium formate at highest tested concentrations did not inhibit the growth of E. coli, S. typhimurium, and E. faecalis but the compound inhibited the growth of other tested bacteria with MIC values from 0.20 to 1.88 mg/L. The MIC values of monovalerin, monolaurin, and monobutyrin ranged between 0.001 and 1.50 mg/L on all bacterial strains with the exception that monobutyrin did not inhibit C. jejuni (ATCC 33560) growth at the highest concentration tested (5.0 mg/L). Monopropionin at tested concentrations did not inhibit the growth of all tested bacteria with the exception of 1.13 mg/L as MIC on C. perfringens (ATCC 12915). The MIC tests indicate that all organic acids and their derivatives, except monopropionin, tested in this experiment exhibited strong antimicrobial effects in vitro against tested bacterial strains.