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Title: The antibacterial action of short and long chain quaternary ammonium compounds
Author: Acheampong, Y. B.
Awarding Body: University of Bradford
Current Institution: University of Bradford
Date of Award: 1980
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Investigations into uptake of alkyl dimethylbenzylammonium compounds by Escherichia coli, their effects on growth, viability, respiration and cellular permeability were studied in a MOPS buffered minimal salts medium. The adsorption isotherms of the long chain tetradecyl compound (ADB-14) and the short chain nonyl compound (ADB-9) by cells suspended in glucose free medium give two distinct regions described as primary and secondary uptakes. In general larger concentrations of ADB-9 are needed to achieve uptake levels comparable to those of ADB-14. The primary uptake is S-shaped and terminates at a plateau during which the analyses of the uptake results suggest there is a formation of a double layer of solute molecules closely packed around each cell. The secondary phase of the isotherm commences at the end of the primary plateau and finally terminates at a "saturation" plateau, which begins when the concentrations of ADB-9 and ADB-14 remaining in solution are approximately equal to the critical micelle. concentrations in the medium as measured by Du NoUy tensiometer. At the primary and the "saturation" plateaux approximately equal amounts of ADB-9 and ADB-14 are taken up by the cell suspension. Glucose does not have any effect on uptake provided there is no growth. Studies of growth inhibition by measurements of absorbance of cultures at 650nm indicate that despite the large concentration of ADB-9 needed, small uptake level comparable to that of ADB-14 is required to cause maximum inhibition of growth. The minimum concentration of ADB-14 to inhibit growth depends on the size of inoculum used whilst that of ADB-9 is not cell density dependent. Viability studies show that glucose influences the bactericidal effects of the compounds, but the influence is more pronounced in ADB-9. Employing an oxygen electrode apparatus to measure oxygen uptake in the presence of glucose, the results suggest that bacteriostatic and bactericidal concentrations of the quaternary ammonium compounds rapidly inhibit oxidative processes in the cell. Maximum inhibition of respiration occurred at bactericidal concentrations. The addition of the agents to washed cell suspensions accelerates the leakage of low molecular weight cell constituents. The effect of ADB-14 concentration on leakage is diphasic; a maximum leakage occurs at a certain concentration beyond which there is inhibition of the process. In contrast, ADB-9 does not cause anyinhibition of leakage with respect to increasing concentration of the agent. There is a linear relationship between the amounts of materials leaked and the percentage of cells killed in the presence of ADB-9 concentrations, and those of ADB-14 less than that causing maximum leakage. ADB-9 does not affect cellular permeability at 2°C. Measurement of turbidity changes in washed cell suspensions at 650nm shows that ADB-14 induces turbidity increase at concentrations beyond which maximum leakage occurs. The use of the mechanism of uptake and the isotherms in the interpretation of the antibacterial actions of ADB-9 and ADB-14 is considered. A review of the evidence obtained in this study reveals that the dodecyl and the tetradecyl compounds act similarly but differ from the nonyl compound. The differences in activities of the compounds are discussed in terms of their capacity to bind and to cause damage to the cell membrane
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Organic chemistry