FIG. 1.

Augmentation of killing of L. monocytogenes at pH 3 and 4 by ethanol combined with various organic acids. Cells grown to the stationary phase (approximately 3 × 10⁹ CFU ml⁻¹) were diluted 1:100 in challenge media at pH 3 or 4 containing either no organic acid (● and ○), dl-lactate (▴ and ▵), dl-malate (■ and □), formate (⧫ and ◊), sorbate (▾ and ▿), or benzoate (▸ and ▹), and viability was assessed. Cells were incubated in the presence (open symbols) or in the absence (solid symbols) of 5% ethanol. For each acid the concentration added at pH 3.0 and 4.0 was the same, and the values shown represent the amounts of undissociated acid. The data are means, and the error bars indicate standard deviations for experiments performed at least in triplicate. The arrows indicate sampling times when no survivors were detected for ethanol combined with organic acids. The limit of detection was 250 CFU ml⁻¹.