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Appl. Environ. Microbiol., Apr 1997, 1252-1255, Vol 63, No. 4
Y Lou and AE Yousef
A sublethal dose of ethanol (5%, vol/vol), acid (HCl, pH 4.5 to 5.0), H2O2
(500 ppm), or NaCl (7%, wt/vol) was added to a Listeria monocytogenes
culture at the exponential phase, and the cells were allowed to grow for 1
h. Exponential-phase cells also were heat shocked at 45 degrees C for 1 h.
The stress-adapted cells were then subjected to the following factors at
the indicated lethal levels--NaCl (25%, wt/vol), ethanol (17.5%, vol/vol),
hydrogen peroxide (0.1%, wt/vol), acid (pH 3.5), and starvation on 0.1 M
phosphate buffer at pH 7.0 (up to 300 h). Viable counts of the pathogen,
after the treatment, were determined on Trypticase soy agar-yeast extract,
and survivor plots were constructed. The area (h.log10 CFU/ml) between the
control and treatment curves was calculated to represent the protective
effect resulting from adaptation to the sublethal stress factor. Adaptation
to pH 4.5 to 5.0 or 5% ethanol significantly (P < 0.05) increased the
resistance of L. monocytogenes to lethal doses of acid, ethanol, and H2O2.
Adaptation to ethanol significantly (P < 0.05) increased the resistance
to 25% NaCl. When L. monocytogenes was adapted to 500 ppm of H2O2, 7% NaCl,
or heat, resistance of the pathogen to 1% hydrogen peroxide increased
significantly (P < 0.05). Heat shock significantly (P < 0.05)
increased the resistance to ethanol and NaCl. Therefore, the occurrence of
stress protection after adaptation of L. monocytogenes to environmental
stresses depends on the type of stress encountered and the lethal factor
applied. This "stress hardening" should be considered when current food
processing technologies are modified or new ones are developed.
Copyright © 1997, American Society for Microbiology
Adaptation to sublethal environmental stresses protects Listeria monocytogenes against lethal preservation factors
Department of Food Science and Technology, Ohio State University, Columbus 43210, USA.
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