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Applied and Environmental Microbiology, July 1999, p. 3048-3055, Vol. 65, No. 7
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.

Survival of Low-pH Stress by Escherichia coli O157:H7: Correlation between Alterations in the Cell Envelope and Increased Acid Tolerance

Kieran N. Jordan,1,2 Lynn Oxford,1 and Conor P. O'Byrne1,*

Microbiology Department, Unilever Research Colworth, Sharnbrook, Bedfordshire MK44 1LQ, England,1 and TEAGASC, National Dairy Products Research Centre, Moorepark, Fermoy, County Cork, Ireland2

Received 17 September 1998/Accepted 15 April 1999

Survival of a nontoxigenic isolate of Escherichia coli O157:H7 at low pH (pH 3.0) was examined over prolonged time periods for each of three population types: exponential-phase cells, stationary-phase cells, and acid-adapted exponential-phase cells. In each population, approximately 5 × 104 CFU ml-1 were detected after a 24-h incubation at pH 3.0. Even after 3 days at pH 3.0, significant numbers of survivors from each of the three populations could be detected. The high level of acid tolerance exhibited by these survivors was found to be quickly lost once they were transferred to conditions which permitted growth to resume, indicating that they were not mutants. Proton flux measurements on the three populations of cells revealed that the initial rates of viability loss at pH 3.0 correlated well with net proton accumulation. Cells showing a high initial rate of viability loss (exponential-phase cells) accumulated protons at the highest rate, whereas resistant populations (adapted or stationary-phase cells) accumulated protons only slowly. Differences in the protein composition of the cell envelope between the three populations were studied by two-dimensional polyacrylamide gel electrophoresis. Complex differences in the pattern of proteins expressed by each population were uncovered. The implications of these findings are discussed in the context of a possible model accounting for acid tolerance in this important food-borne pathogen.

* Corresponding author. Present address: Department of Molecular and Cell Biology, Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, Scotland. Phone: (44 1224) 273151. Fax: (44 1224) 273144. E-mail: mbi106{at}abdn.ac.uk.

Applied and Environmental Microbiology, July 1999, p. 3048-3055, Vol. 65, No. 7
0099-2240/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.


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