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Applied and Environmental Microbiology, April 2001, p. 1594-1600, Vol. 67, No. 4
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.4.1594-1600.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

Sensitization of Listeria monocytogenes to Low pH, Organic Acids, and Osmotic Stress by Ethanol

Clive Barker and Simon F. Park*

School of Biological Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom

Received 28 August 2000/Accepted 29 January 2001

The killing of Listeria monocytogenes following exposure to low pH, organic acids, and osmotic stress was enhanced by the addition of 5% (vol/vol) ethanol. At pH 3, for example, the presence of this agent stimulated killing by more than 3 log units in 40 min of exposure. The rate of cell death at pH 3.0 was dependent on the concentration of ethanol. Thus, while the presence 10% (vol/vol) ethanol at pH 3.0 stimulated killing by more than 3 log units in just 5 min, addition of 1.25% (vol/vol) ethanol resulted in less than 1 log unit of killing in 10 min. The ability of 5% (vol/vol) ethanol to stimulate killing at low pH and at elevated osmolarity was also dependent on the amplitude of the imposed stress, and an increase in the pH from 3.0 to 4.0 or a decrease in the sodium chloride concentration from 25 to 2.5% led to a marked reduction in the effectiveness of 5% (vol/vol) ethanol as an augmentative agent. Combinations of organic acids, low pH, and ethanol proved to be particularly effective bactericidal treatments; the most potent combination was pH 3.0, 50 mM formate, and 5 % (vol/vol) ethanol, which resulted in 5 log units of killing in just 4 min. Ethanol-enhanced killing correlated with damage to the bacterial cytoplasmic membrane.

* Corresponding author. Mailing address: School of Biological Sciences, University of Surrey, Guildford GU2 7XH, United Kingdom. Phone: 44 (0)1483 879024. Fax: 44 (0)1483 300374. E-mail: s.park{at}surrey.ac.uk.

Applied and Environmental Microbiology, April 2001, p. 1594-1600, Vol. 67, No. 4
0099-2240/01/$04.00+0   DOI: 10.1128/AEM.67.4.1594-1600.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.


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  • Fang, W., Siegumfeldt, H., Budde, B. B., Jakobsen, M. (2004). Osmotic Stress Leads to Decreased Intracellular pH of Listeria monocytogenes as Determined by Fluorescence Ratio-Imaging Microscopy. Appl. Environ. Microbiol. 70: 3176-3179 [Abstract] [Full Text]  


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