Tracking and controlling Listeria monocytogenes in food processing facilities

Listeria monocytogenes is a serious foodborne pathogen responsible for many deadly outbreaks and costly recalls associated with different types of ready-to-eat (RTE) foods. L. monocytogenes is a challenging problem for the food industry because it grows at refrigeration temperatures and cycles between a saprophyte in nature and a pathogen of animals, including humans. Individual food processing plants are typically colonized by their own unique clone of L. monocytogenes, which may persist for decades. These persistent clones may have adapted to the type of food in each facility and thus repeatedly contaminate RTE foods. Reservoirs for Listeria monocytogenes often are wet, difficult to clean areas (harborage sites) within the processing facility, which allows L. monocytogenes to grow to high levels and form biofilms. When inside a biofilm many cells enter a dormant long-term-survival phase, where they are more tolerant to numerous stresses, including sanitizers. Harborage sites include wet, porous non-food-contact surfaces like floors and drains, as well as cracked, pitted or other difficult-to-clean food-contact surfaces. L. monocytogenes can survive normal cleaning and sanitizing programs when located deep within such harborage sites, and come out again during operation to cause food contamination. Epidemic clones and outbreak clones of this pathogen can be accurately detected and tracked using Multi-Virulence-Locus Sequence Typing (MVLST) developed in my laboratory. Control of contamination depends upon detecting and eliminating harborage sites within the food processing facility, especially those containing dangerous persistent clones. Continuous monitoring and elimination of such harborage sites will prevent contamination and ensure food safety.