Adaptation to sublethal environmental stresses protects Listeria monocytogenes against lethal preservation factors

Abstract

A sublethal dose of ethanol (5%, vol/vol), acid (HCl, pH 4.5 to 5.0), H 2 O 2 (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؇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 in 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 ⅐ log 10 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 H 2 O 2 . Adaptation to ethanol significantly (P < 0.05) increased the resistance to 25% NaCl. When L. monocytogenes was adapted to 500 ppm of H 2 O 2 , 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.

Genetic and environmental factors influence Listeria monocytogenes nisin resistance

“…Listeria monocytogenes encounters numerous environmental stresses during transmission from food to humans, and there are many examples where exposure to one stress influences the ability of the pathogen to grow or survive upon exposure to a subsequent stress. For example, exposure to acidic pH can lead to increased resistance to subsequent exposure to lethal concentrations of H 2 O 2 and ethanol (Lou and Yousef 1997). Exposure of L. monocytogenes to osmotic stress can lead to cross-protection against other stresses, such as low temperature (Schmid et al 2009) and bile salts (Begley et al 2002).…”

Ethanol adaptation induces direct protection and cross-protection against freezing stress in Salmonella enterica serovar Enteritidis

“…Hence, there exist opportunities for pathogens to adapt and grow under mild ethanol stress. Ethanol adaptation has been reported to induce direct protection and/or cross-protection against various environmental stresses in several food-borne pathogens, including Listeria monocytogenes (Lou and Yousef 1997), Vibrio parahaemolyticus (Chiang et al 2006(Chiang et al , 2008Chiang and Chou 2009) and Cronobacter sakazakii (Huang et al 2013). This may counteract the effectiveness of currently employed food control measures, thus compromising food safety.…”

Response of Listeria monocytogenes to liquid smoke

“…The physico-chemical characteristics of the smoked salmon matrix may have a protective effect against phenolic stress. This may also result from a cross-protection from the other stresses experienced by bacteria during processing and storage (Lou and Yousef 1997).…”