| Escherichia coli has been responsible for a number of food- and water-borne outbreaks. Right now the food industry and regulatory agencies are concerned about control of this organism. Lactic acid is an organic acid frequently used as a food preservative. However, the basis of its antimicrobial action has not been fully established. The overall objective of our research is to increase the understanding of the mechanism of action of lactic acid in terms of important cellular physiological processes leading to death of E. coli K12.; The effect of 1% lactic acid at pH 3.5 on the cell viability, respiration, internal K, Na, Ca, Mg levels, internal pH, internal volume, membrane potential, and proton motive force, macromolecules synthesis and degradation, glucose uptake, cell membrane integrity and genomic DNA has been studied, and compared to cell culture without the addition of lactic acid. The organisms died over a period of three hours. Lactic acid (1% and pH = 3.5) inhibited E. coli K12 metabolism immediately. For example, oxygen was no longer used as a terminal electron acceptor. The addition of lactic acid also rapidly modified chemical and electrical membrane potentials diminishing the ability of the organism to carry out a variety of energy-linked processes. Nevertheless, these potentials did not completely collapse. For example, while the organism was dying, they maintained an intracellular pH near 4.7. Lactic acid caused a significant decrease in intracellular K and resulted in membrane damage. We believe that the damage becomes irreversible and the bacteria die when the cell membrane is damaged and cells lose a permeability barrier. Cell genomic DNA was not oxidized under the acidic condition and the cells did not lyse in the time frame of these experiments. |
