Listeria monocytogenes

Listeria monocytogenes typically causes infection in humans when ready-to-eat food products are contaminated during processing; the bacteria increase in number during refrigerated storage, and then the food is consumed without adequate heating. L. monocytogenes is a nonspore-forming, Gram-positive bacillus that is readily found in both soil and water samples. It mediates its own uptake into nonphagocytic cells via a family of surface-exposed proteins called internalins. Orally transmitted models of L. monocytogenes infection have not been as widely used as intravenous or intraperitoneal models due to a high degree of innate resistance in many species and significant phenotypic variability among infected animals. Recent improvements, particularly for the mouse model, have greatly improved the efficiency of intestinal infection following oral transmission, and the use of a standardized model would help to greatly advance the field. Studies that directly compare infections in young versus aged animals may shed light on potential therapeutic strategies that could prevent these deadly infections.