General Mechanism of Pathogenesis

Abstract

Foodborne pathogens cause three forms of disease: foodborne infection, foodborne intoxication, and foodborne toxicoinfection. The principal route of infection/intoxication for foodborne pathogens is oral and the primary site of action is the gastrointestinal tract. The infectious dose of foodborne pathogens varies and depends on the type of organisms or toxin as well as the type of food (liquid vs. solid) ingested. The pathogens that are responsible for infection colonize the gut by producing various adhesion factors including fimbriae, curli, adhesin proteins, and extracellular matrices that allow biofilm formation. Invading pathogens have developed strategies to cross the epithelial barrier. Some use M cells to reach the subcellular location or some pathogens actively penetrate epithelial cells by rearranging the host cell cytoskeletal structure. Pathogens localized in the subcellular locations multiply, move from cell-to-cell, and induce inflammation and elicit cell damage to induce diarrhea and gastroenteritis. Some intracellular pathogens induce apoptosis or necrosis in macrophages, dendritic cells, neutrophils, and other cells, thus ensuring their survival in host tissues. Pathogens may also translocate to deeper tissues including the liver, lymph nodes, spleen, brain, and placenta. Foodborne intoxication is mediated by exotoxins produced by pathogens in the food, which induces cell damage, fluid and electrolyte losses, and apoptosis or blocks nerve impulse following consumption of the contaminated food. The mechanisms of exotoxin action may vary, and based on the toxin action, the toxins can be classified as A–B type toxins, membrane-acting toxins, superantigens, proteases, protein synthesis inhibitors, and signal transduction modulators. The bacterial cell wall or membrane-associated endotoxins (LPS, PGN) are generally associated with systemic foodborne infection, and these toxins modulate the immune system to induce the release of large quantities of cytokines that promote fever, decrease blood pressure, and induce septic shock. In most pathogens, virulence factors encoded genes are located in pathogenicity islands or islets, which may be found on plasmids, bacteriophage, or the chromosome. Virulence proteins are exported from the microbes by various secretory machinary and those are designated type I–type VII and Sec secretory systems. Finally, bacterial virulence gene expression is a complex process that may be controlled by different regulatory elements in the food system as well as in the host. Alternate sigma factors are found to be crucial in virulence gene expressions in foodborne pathogens.