Effect of Metal Cations and pH on the Antibacterial Activity and Uptake of Long Chain Fatty Acids

Abstract

The bactericidal activity of long chain saturated fatty acids was antagonized by alkaline earth metals. The activity of linoleic acid waa less effectively antagonized but was more sensitive to reversal by ferric and stannous ions. With increasing pH value the bactericidal activity of lauric acid decreased but that of the longer chain saturated acids increased. Both Gram positive and Gram negative bacteria reversibly adsorbed fatty acids, Uptake increased with decreasing pH value and increasing chain length. Although adsorbed to a lesser extent, the intrinsic activity of linoleic acid was greater than lauric acid. The uptake appeared to be non-specSc and governed by the physicochemical properties of both the a i d s and the bacterial cell surfaces. Sensitivity to the fatty acids increased with decreasing pH value. Protoplasts of Bacillus mqaterium adsorbed fatty acids to a greater extent than whole cells. Resistance of the Gram negative Pseudomonas p k e o l i w l a was not due t o non-adsorption of the fatty acids. H. Galbraith and T. B. Miller ChemkdsFatty acids (l-14C labelled) were obtained from the Radiochemical Centre, Amersham, England. Lysozyme was a product of Sigma Ltd. Koch-Light Co. Ltd supplied the scintillation grade PPO (2,5 diphenyloxazole), POPOP [1,4-di(2-(5-phenyloxazolyl)) benzene] and naphthalene. The Maybridge Chemical Co. (Scarne Industrial Estate, Launceston, England) supplied the 2,4 dioxan which was double-distilled prior to use. All other chemicals were Analar grade or as previously specified (Galbraith et al., 1971). Preparation of organismsThe bacteria were grown, harvested and suspended in the buffered test systems as described by Galbraith et al. (1971), for bactericidal studies. Similarly, cations were added (as chlorides) and bactericidal activities estimated as before. Volumes (0.5 ml) of the bacterial suspension (c 1-2 x lo9 cells/ml) were added to 2.5 ml of the particular test system. Buffer solutionsPhosphate buffer at pH 6.0 and Tris-HC1 buffers at pH 7.0 to 8.0 were prepared at 0.1 M concentration by the method of Cruickshank (1968). The effect of cations was studied at pH 7.0 to 8.0 to avoid the precipitation found with phosphate buffers. Preparation of protoplustsProtoplasts of B. megaterium were prepared by a method similar to that of Baird-Parker & Woodroffe (1967). Cells (c. 1.2 x 109/ml) were suspended at pH 7.0 in 0.1 M Tris-buffered 0.5 M sucrose containing 30 pg/ml of lysozyme and 25 mM-NaC1 at 30". Microscopic examination showed that removal of the cell wall was complete at 25 min after which the protoplasts were sedimented by centrifuging (1000 g for 15 min) and gently resuspended to the original volume in the required buffer, containing 0-5 M sucrose and 2-5 m-NaC1. Where used, 0.5 ml of this suspension was added to 2.5 ml of the isotonic test system. Measurement of radioactivityRadioactivity was counted on a Beckman LS-150 liquid scintillation counter using 10 ml volumes of the scintillation solution containing naphthalene, 100 g; PPO, 5 g ; POPOP, 0.3 g/1 of 2,...

In vitro ruminal methane suppression by lauric acid as influenced by dietary calcium

“…The latter suggests that significant soap formation with C 12:0 had taken place. The reversal of the antibacterial activity of MCFA by Ca supplementation is well documented for C 12:0 (Galbraith et al 1971) and C 14:0 (Galbraith and Miller 1973). Furthermore, Koster (1987) demonstrated that the inhibition of the methanogenic population in biogas reactors due to C 12:0 could be reversed by the addition of an equimolar amount of Ca ions, but only when added together with the fatty acids.…”

Perspectives on ruminant nutrition and metabolism I. Metabolism in the Rumen

“…The presence of calcium ions and, to a lesser extent, magnesium ions is known to reduce the antimicrobial action of LCFA (Galbraith & Miller, 1973). Inclusion of calcium hydroxide in ruminant diets makes it possible to increase rates of fat inclusion substantially without adverse effects on fibre digestibility (Palmquist, 1988;Ohajuruka et al 1991).…”

Effect of pH on Bactericidal Activities of Calcium Laurate

“…Short-chain fatty acids are more active at low than at higher pH 10 . Galbraith et al reported that the bactericidal activity of lauric acid decreased with increasing pH value but that of myristic acid and palmitic acid increased 11 . However, the effect of pH on the bactericidal activity of the surfactant calcium salt is largely unknown.…”