# Stress-Driven Tolerance and Persistence of Listeria monocytogenes Across the Farm-to-Fork Continuum

## TL;DR

This paper explains how repeated nonlethal stresses during food handling can make Listeria monocytogenes harder to detect and eliminate, affecting food safety.

## Contribution

The paper introduces stress history as a core factor in understanding bacterial persistence and detection limitations in food systems.

## Key findings

- Repeated sublethal stress can shift bacterial populations toward stress-hardened states without genetic adaptation.
- Stress-hardened states include biofilm formation, viable but nonculturable cells, and increased tolerance to later stresses.
- Current monitoring methods may underestimate viable cells due to limited recovery of pre-stressed bacteria.

## Abstract

As food moves from farms to consumers, bacteria are exposed to many everyday stresses. These include refrigeration, drying, cleaning chemicals, and food processing steps. These stresses do not always kill bacteria. Instead, they can change how bacteria behave. Some cells recover slowly, hide in biofilms, or enter dormant states that routine tests cannot easily detect. This review explains how repeated stress affects bacterial survival, using Listeria monocytogenes as a key example. We show how stress history helps explain why Listeria can persist in food-processing environments, reappear after cleaning, and sometimes escape detection. Understanding how bacteria respond to stress in real food systems can improve monitoring, sanitation, and food safety decisions.

Food systems expose bacteria to repeated nonlethal stresses during primary production, processing, storage, and sanitation. Depending on the type, intensity, and sequence of exposure, these stresses may weaken cells, act synergistically to promote inactivation, or fail to eliminate contamination. Instead, they can alter bacterial physiology in ways that affect survival, recovery, detection, and responses to control measures. This review examines how stress history contributes to persistent food safety challenges. Listeria monocytogenes is used as a central biological model, with relevant comparisons to other foodborne pathogens. Evidence from food-processing and environmental studies shows that repeated sublethal stress can shift bacterial populations toward stress-hardened states. Here, “stress-hardened” refers to reversible physiological changes and the survival of more tolerant cells, not permanent genetic adaptation. These states include sublethal injury, delayed growth, viable but nonculturable cells, biofilm formation, and increased tolerance to later stresses. These outcomes contribute to, but do not fully explain, the persistence of L. monocytogenes in food environments; intrinsic traits such as psychrotrophic growth and interactions with endogenous microflora also play important roles. These factors help explain repeated recovery of L. monocytogenes after sanitation and the underestimation of viable cells by routine culture-based methods, which do not reliably indicate whether pre-stressed cells retain the potential to cause foodborne illness. Many monitoring and validation approaches rely on unstressed laboratory cultures and fixed enrichment protocols. These conditions do not reflect the physiological states encountered in real food systems. As a result, negative test results may reflect limited recovery rather than true absence, and control performance may be overestimated when stress-conditioned populations are not considered. Across the farm-to-fork continuum, stress responses, persistence mechanisms, and detection limitations are closely linked, indicating that stress history should be considered a core element of hazard characterization, monitoring, and control validation. Incorporating stress biology into food safety assessment can improve the realism of verification strategies when combined with risk characterization that considers infectious dose and host susceptibility, and support control strategies under real-world processing and environmental conditions.