Molecular biology of surface colonization by Listeria monocytogenes: an additional facet of an opportunistic Gram‐positive foodborne pathogen

Abstract

SummaryThe opportunistic and facultative intracellular pathogenic bacterium Listeria monocytogenes causes a rare but severe foodborne disease called listeriosis, the outcome of which can be fatal. The infection cycle and key virulence factors are now well characterized in this species. Nonetheless, this knowledge has not prevented the re-emergence of listeriosis, as recently reported in several European countries. Listeria monocytogenes is particularly problematic in the food industry since it can survive and multiply under conditions frequently used for food preservation. Moreover, this foodborne pathogen also forms biofilms, which increase its persistence and resistance in industrial production lines, leading to contamination of food products. Significant differences have been reported regarding the ability of different isolates to form biofilms, but no clear correlation can be established with serovars or lineages. The architecture of listerial biofilms varies greatly from one strain to another as it ranges from bacterial monolayers to the most recently described network of knitted chains. While the role of polysaccharides as part of the extracellular matrix contributing to listerial biofilm formation remains elusive, the importance of eDNA has been demonstrated. The involvement of flagella in biofilm formation has also been pointed out, but their exact role in the process remains to be clarified because of conflicting results. Two cell-cell communication systems LuxS and Agr have been shown to take part in the regulation of biofilm formation.Several additional molecular determinants have been identified by functional genetic analyses, such as the (p)ppGpp synthetase RelA and more recently BapL. Future directions and questions about the molecular mechanisms of biofilm formation in L. monocytogenes are further discussed, such as correlation between clonal complexes as revealed by MLST and biofilm formation, the swarming over swimming regulation hypothesis regarding the role of the flagella, and the involvement of microbial surface components recognizing adhesive matrix molecules in the colonization of abiotic and biotic surfaces.

comK Prophage Junction Fragments as Markers for Listeria monocytogenes Genotypes Unique to Individual Meat and Poultry Processing Plants and a Model for Rapid Niche-Specific Adaptation, Biofilm Formation, and Persistence

“…Many authors have speculated that biofilm formation is the reason for the persistence of specific strains in food processing plants. However, other explanations for this phenomenon have also been suggested, including continual reintroduction of the same strain over extended periods of time, random primary colonization, ability to grow and survive at low temperatures, competitiveness for nutrients, ability to mount a stringent response and undergo physiological adaptation to nutrient deprivation, resistance to sanitizers and/or heavy metals and antibiotics, ability to interact with other microorganisms to form a stable ecosystem within biofilms, or some combination of the above (70,78,83,105).…”

“…Cells of L. monocytogenes within biofilms are more resistant to biocides (102), which increases the risk of food contamination. Initial adherence is critical for biofilm formation and depends on the physiochemical properties of the environmental surfaces as well as the biofilm-forming potential of the bacterial cells (18,83,102). L. monocytogenes can adhere to abiotic surfaces such as stainless steel, glass, plastic, polymers, and rubber that are present in the food processing environment (44,102,107).…”

Exploring the Diversity of Listeria monocytogenes Biofilm Architecture by High-Throughput Confocal Laser Scanning Microscopy and the Predominance of the Honeycomb-Like Morphotype

“…Biofilms of L. monocytogenes are associated with important ecological advantages, such as protection against biocide action (7). Several molecular determinants, such as flagella, biofilm-associated proteins (Bap), SecA2, and cell-cell communication systems, have been shown to be involved in biofilm construction within the species (8,9). While no exopolysaccharidic components have been evidenced in the L. monocytogenes biofilm matrix (8), extracellular DNA (eDNA) has been shown to participate in initial cellular adhesion and biofilm organization under specific growth conditions (10).…”

Actin Polymerization Drives Septation of Listeria monocytogenes namA Hydrolase Mutants, Demonstrating Host Correction of a Bacterial Defect

“…The Gram-positive bacterium Listeria monocytogenes is an environmental pathogen that is capable of orchestrating a complex transition from life in the outside environment to life within the cytosol of an infected host (18,30,51). As an environmental bacterium, L. monocytogenes survives in a number of diverse settings, including soil, water, and silage (51,60).…”

“…As an environmental bacterium, L. monocytogenes survives in a number of diverse settings, including soil, water, and silage (51,60).…”