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Applied and Environmental Microbiology, December 2003, p. 7514-7516, Vol. 69, No. 12
0099-2240/03/$08.00+0 DOI: 10.1128/AEM.69.12.7514-7516.2003
Copyright © 2003, American
Society for
Microbiology. All Rights Reserved.
Patricia A. Kendall, and John N. Sofos*
Center for Red Meat Safety, Department of Animal Sciences, and Department of Food Science and Human Nutrition, Colorado State University, Fort Collins, Colorado 80523
Received 10 April 2003/ Accepted 8 September 2003
Stationary-phase cells of Listeria monocytogenes grown in glucose-free or glucose-containing media were exposed for 90 min to various stresses, including acid stress (pH 4.0 to 7.0), osmotic stress (10.5 to 20.5% NaCl), and various temperatures (-5 to 50°C), and were further exposed to pH 3.5. Exposure to a mildly acidic (pH 5.0 to 6.0) environment provided protection of the pathogen against acid upon subsequent exposure. This adaptive response, however, was found to be strongly dependent on other environmental conditions during the shock, such as temperature or the simultaneous presence of a second stress factor (NaCl). Growth of L. monocytogenes in the presence of glucose resulted in enhanced survival of the pathogen at pH 3.5. Sublethal stresses other than acidic stresses, i.e., osmotic, heat, and low-temperature stresses, did not affect the acid resistance of L. monocytogenes (P > 0.5). More-severe levels of these stresses, however, resulted in sensitization of the pathogen to acid.
Present
address: Aristotle University of Thessaloniki, Faculty of Agriculture,
Department of Food Science and Technology, Thessaloniki 54124,
Greece.
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