Inhibitory Action of Fatty Acids on the Growth of Neisseria gonorrhoeae

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Abstract
Fatty acids of various chain lengths (C 1 to C 24 ) were examined for their effects on growth, oxygen consumption, and in vitro reduced nicotinamide adenine dinucleotide oxidase activity of Neisseria gonorrhoeae CS-7. The growth inhibition caused by saturated fatty acids increased with increasing chain length to a maximum with palmitic acid (C 16 ). Stearic acid (C 18 ) and longer saturated fatty acids showed little inhibition of growth. However, unsaturated fatty acids of chain length C 16 to C 20 were inhibitory. Similar inhibition was observed with Bacillus subtilis and a deep rough mutant of Salmonella typhimurium. Wildtype S. typhimurium and Pseudomonas aeruginosa were more resistant to medium-chain (C 7 to C 10 ) fatty acids and completely resistant to long-chain (C 12 to C 18 ) fatty acids. Thus, sensitivity of N. gonorrhoeae to long-chain fatty acids appears to be related to the permeability of the outer membrane. Growth inhibition by short-chain (C 1 to C 6 ) fatty acids was pH dependent; inhibition of growth increased with decreasing pH. Saturated fatty acids inhibited oxygen consumption by log-phase cells of N. gonorrhoeae. This inhibition increased with increasing chain length to a maximum observed with myristic acid (C 14 ). Whereas stearic acid (C 18 ) had little effect upon oxygen consumption, unsaturated C 18 fatty acids were inhibitory. An in vitro inhibition of reduced nicotinamide adenine dinucleotide oxidase activity by saturated (C 1 to C 12 ) and unsaturated (C 16 to C 20 ) fatty acids was also observed. Although the inhibitory concentrations were generally higher than those required to inhibit growth or oxygen consumption, an inhibition of electron transport may be partially responsible for the observed growth inhibition.