Shigella flexneri inhibition by acetic acid

Area of Science:

• Microbiology
• Biochemistry

Background:

• Acetic acid is a weak acid with known antimicrobial properties.
• Shigella flexneri is a Gram-negative bacterium that causes bacillary dysentery.

Purpose of the Study:

• To investigate the mechanism by which acetic acid inhibits Shigella flexneri growth.
• To determine the critical concentration of undissociated acetic acid for inhibition.
• To elucidate the cellular processes affected by acetic acid.

Main Methods:

• Bacterial growth inhibition assays in a chemically defined medium.
• Measurement of intracellular accumulation of glucose, glutamic acid, and phosphate.
• Uptake studies using a glucose analogue (3-o-methyl-D-glucose).
• Respiration studies with cell-free extracts.

Main Results:

• Inhibition of S. flexneri growth was dependent on the concentration of undissociated acetic acid.
• A critical concentration of approximately 0.0018 M undissociated acetic acid completely inhibited bacterial multiplication.
• Reversal of inhibition was achieved by increasing the medium pH.
• Acetic acid interfered with intracellular glucose and glutamic acid accumulation but not phosphate.
• Acetic acid did not inhibit the uptake of a glucose analogue, suggesting interference with metabolism rather than permeation.
• Respiration studies confirmed a metabolic block caused by acetic acid.

Conclusions:

• Acetic acid inhibits Shigella flexneri by interfering with glucose metabolism.
• The undissociated form of acetic acid is more permeable to bacterial cells.
• The pH of the medium significantly influences the inhibitory effect of acetic acid on bacterial growth.