The relationship between the uptake and antimicrobial activity of p-hydroxybenzoic acid esters (parabens) was studied using Escherichia coli. The uptake into bacterial cells and the antibacterial activity of parabens were logarithmically proportional to the carbon number of the alkyl group from methyl to butyl paraben. The free energy change for the transfer of the methylene group of parabens from the aqueous to the cell phase was less than that obtained from the n-hexane and n-octanol-water partition systems. This demonstrates that the hydrophilicity of the cells is larger than n-hexane and n-octanol. The uptake of hydrophobic ethyl benzoate was less than that of the more hydrophilic butyl paraben possessing a phenolic hydroxyl group. Parabens may thus be incorporated into cells by both hydrophobic and hydrophilic interactions. The apparent concentration of parabens in the bacterial cells required to produce the same antibacterial activity decreased logarithmically with an increasing carbon number of the alkyl group. The dependence of the antibacterial activity of parabens on the alkyl chain length may thus be concluded to be due to the alkyl group, not only for uptake into bacterial cells but also for accumulation or concentration on biological receptors after incorporation into the cells.
The enhancing effects of maltitol (alpha-D-glucopyranosyl-1,4-sorbitol) on absorption of calcium by the rat intestine have been studied by use of [45Ca]CaCl2 in-vivo. After intragastric administration of [45Ca]CaCl2 solution with maltitol, plasma 45Ca concentration remained at the maximum level for more than 80 min, whereas for animals given [45Ca]CaCl2 solution without maltitol, plasma 45Ca concentration declined sharply after the peak. Determination of 45Ca radioactivity remaining in the various segments of the gastrointestinal tract revealed that administration of maltitol elicited slower gastric emptying and slower intestinal transit, resulting in extensive 45Ca distribution along the small intestine throughout the experimental period. The luminal contents of the small intestine were significantly higher in rats given maltitol than in the control group. These results suggest that the enhancing action of maltitol on intestinal calcium absorption could be attributed to reduced gastrointestinal calcium transit and increased luminal fluid content, presumably because of the osmotic activity of maltitol; this would not only accelerate the dissolution of calcium into the increased luminal contents, but also enable a larger area of the small intestine to absorb calcium for a longer period of time.
The effects of polyoxyethylene cetyl ether (PCE) on the cellular uptake and the antibacterial activity of butyl p-hydroxybenzoate (BP) by bacteria were studied using an aqueous suspension of Escherichia coli. The BP in the cell suspension was distributed in the cells and aqueous phase. PCE added to the BP solution was responsible for reducing the BP uptake into the cells and inhibiting the antibacterial activity of BP due to the formation of a complex between BP and PCE micelles. The uptake and antibacterial activity of BP were proportional to the unbound BP concentration in the aqueous bulk solution. However, the addition of PCE repressed BP uptake in the cells and enhanced BP activity compared with those values expected from unbound BP in the aqueous surfactant solution. These results suggested that direct interactions between PCE and bacterial cells increased the susceptibility of bacteria. The decrease in BP uptake into bacterial cells was thus concluded to be responsible for the reduction in the antibacterial activity of BP in an aqueous surfactant solution, and the measurement of paraben uptake by microbial cells was found to be a reliable means for assessing inactivation in an aqueous solution in the presence of surfactants.
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