Stress responses

Considering that L. monocytogenes appears to be a normal resident of the human and animal intestinal tract, with 8-10% of the general population and 1-5% of animals being carriers,⁸ it is not surprising that L. monocytogenes is found so routinely in the environment, being shed in the feces of its mammalian hosts.^1-4,9 Any successful pathogen must be able to surmount the numerous stresses it encounters during its life cycle-from the natural environment to the food processing plant and, nally, within the mammalian host. After evacuating the host, L. monocytogenes experiences a number of arduous conditions, such as a temperature downshift and possible uctuations in pH and osmolarity, followed by a variety of progressively serious nutrient limitations. Conversely, L. monocytogenes may survive and multiply within protozoans, a normal inhabitant of the natural environment, providing a more favorable milieu while allowing the pathogen to adapt for survival within the mammalian host.¹⁰ The high frequency with which L. monocytogenes is found in the environment, coupled with its ability to survive and multiply under conditions frequently used for food preservation (such as dehydration, freezing, freeze-thawing, refrigeration, heat, low pH, and salt¹¹), makes this pathogen particularly problematic to the food industry and a great risk to human and animal health.