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Applied and Environmental Microbiology, April 1999, p. 1564-1569, Vol. 65, No. 4
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Variation in Resistance of Natural Isolates of Escherichia coli O157 to High Hydrostatic Pressure, Mild Heat, and Other Stresses

Amparo Benito, Georgia Ventoura, Maria Casadei, Tobin Robinson, and Bernard Mackey*

Institute of Food Research, Earley Gate, Reading RG6 6BZ, United Kingdom

Received 31 August 1998/Accepted 20 January 1999

Strains of Escherichia coli O157 isolated from patients with clinical cases of food-borne illness and other sources exhibited wide differences in resistance to high hydrostatic pressure. The most pressure-resistant strains were also more resistant to mild heat than other strains. Strain C9490, a representative pressure-resistant strain, was also more resistant to acid, oxidative, and osmotic stresses than the pressure-sensitive strain NCTC 12079. Most of these differences in resistance were observed only in stationary-phase cells, the only exception being acid resistance, where differences were also apparent in the exponential phase. Membrane damage in pressure-treated cells was revealed by increased uptake of the fluorescent dyes ethidium bromide and propidium iodide. When strains were exposed to the same pressure for different lengths of time, the pressure-sensitive strains took up stain sooner than the more resistant strain, which suggested that the differences in resistance may be related to susceptibility to membrane damage. Our results emphasize the importance of including stress-resistant strains of E. coli O157 when the efficacy of a novel or mild food preservation treatment is tested.

* Corresponding author. Mailing address: Institute of Food Research, Earley Gate, Reading RG6 6BZ, United Kingdom. Phone: 44 118 935 7229. Fax: 44 118 935 7222. E-mail: bernard.mackey{at}bbsrc.ac.uk.

Applied and Environmental Microbiology, April 1999, p. 1564-1569, Vol. 65, No. 4
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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Copyright © 1999 by the American Society for Microbiology. All rights reserved.