The Role of Stress and Stress Adaptations in Determining the Fate of the Bacterial Pathogen Listeria monocytogenes in the Food Chain

Abstract

The foodborne pathogen Listeria monocytogenes is a highly adaptable organism that can persist in a wide range of environmental and food-related niches. The consumption of contaminated ready-to-eat foods can cause infections, termed listeriosis, in vulnerable humans, particularly those with weakened immune systems. Although these infections are comparatively rare they are associated with high mortality rates and therefore this pathogen has a significant impact on food safety. L. monocytogenes can adapt to and survive a wide range of stress conditions including low pH, low water activity, and low temperature, which makes it problematic for food producers who rely on these stresses for preservation. Stress tolerance in L. monocytogenes can be explained partially by the presence of the general stress response (GSR), a transcriptional response under the control of the alternative sigma factor sigma B (σB) that reconfigures gene transcription to provide homeostatic and protective functions to cope with the stress. Within the host σB also plays a key role in surviving the harsh conditions found in the gastrointestinal tract. As the infection progresses beyond the GI tract L. monocytogenes uses an intracellular infectious cycle to propagate, spread and remain protected from the host’s humoral immunity. Many of the virulence genes that facilitate this infectious cycle are under the control of a master transcriptional regulator called PrfA. In this review we consider the environmental reservoirs that enable L. monocytogenes to gain access to the food chain and discuss the stresses that the pathogen must overcome to survive and grow in these environments. The overlap that exists between stress tolerance and virulence is described. We review the principal measures that are used to control the pathogen and point to exciting new approaches that might provide improved means of control in the future.

Role and regulation of the stress activated sigma factor sigma B (σB) in the saprophytic and host-associated life stages of Listeria monocytogenes

“…Listeria monocytogenes is a remarkable bacterial pathogen not only because of the sophisticated molecular mechanisms that it uses to invade and colonise the mammalian host (Cossart, 2011;de las Heras, Cain, Bielecka & Vazquez-Boland, 2011;Radoshevich & Cossart, 2018), but also because it is exquisitely well-adapted to cope with a range of environmental challenges including osmotic and acid stresses as well as cold temperatures (Gandhi & Chikindas, 2007;NicAogain & O'Byrne, 2016;O'Byrne & Karatzas, 2008;van Schaik & Abee, 2005). The latter properties make this food-borne pathogen particularly difficult to eliminate from the food chain, especially in so-called ready-to-eat foods, those foods that can be eaten without prior cooking (NicAogain & O'Byrne, 2016). Although infections are not very common in healthy individuals, the high mortality rate associated with infections (de Noordhout et al, 2014;Lecuit, 2007) combined with the ubiquity of this organism in the environment mean that is taken very seriously by food producers and it continues to represent a serious public health risk.…”

Modelling the survival of Listeria monocytogenes strains in soft lactic cheese following acid and salt stress exposures

“…This upward concavity of the curves was a reflection of the quick inactivation of the sensitive subpopulation (Peleg ). For cells subjected to acid and salt stress prior to cheese inoculation, the lack of a sharp decline is an indication that stress exposures result in the development of adaptive stress tolerance responses and cell populations with reduced susceptibility to the food stress (NicAogáin and O’Byrne ).…”

Characterization of the biofilm phenotype of a Listeria monocytogenes mutant deficient in agr peptide sensing

“…Listeria monocytogenes is a saprophytic soil organism that is widespread in nature (Vivant, Garmyn, & Piveteau, ) and frequently found in food processing environments posing a threat to the food chain (Bolocan et al, ; Muhterem‐Uyar et al, ; NicAogáin & O'Byrne, ). In healthy individuals, food‐borne infections with L. monocytogenes result in mild gastroenteritis or remain completely asymptomatic.…”

“…Two characteristics that make L. monocytogenes a major concern in food processing and sanitation of the respective production lines are the ability to form surface-attached communities (also referred to as biofilm formation) and an extremely high tolerance to a wide range of environmental conditions and stresses (Ferreira, Wiedmann, Teixeira, & Stasiewicz, 2014;NicAogáin & O'Byrne, 2016).…”