22:T43d,LISTERIA monocytogeneshas been recognized as a human pathogen for more than 50 years; it causes illness mainly in pregnant women, newborns, elderly persons, and immunocompromised persons. The organism is found in multiple ecological sites and throughout the food chain, and anecdotal reports have linked human illness with the ingestion of foods contaminated withListeria.¹More recently, it has been shown to cause outbreaks of illness that were associated with commercial food products.^2-5The Food and Drug Administration has recommended product recalls whenL monocytogeneshas been identified in commercial foods that are available for consumption without further cooking. Although recalls have generated widespread public concern, information about the magnitude of risk and the clinical presentations of disease has not been widely available to the medical community. This article reviews the history, microbiology, ecology, pathogenesis, epidemiology, and clinical spectrum of human illnesses caused byL monocytogenesand highlights23:T509,The fate of Listeria monocytogenes during refrigerated storage was determined on several processed meat products, including ham, bologna, wieners, sliced chicken, sliced turkey, fermented semidried sausage, bratwurst, and cooked roast beef. The meats were surface inoculated with a five-strain mixture of less than or equal to 200 or ca. 10(5) L. monocytogenes cells per package, vacuum packaged, and stored at 4.4 degrees C. Survival or growth of listeriae was determined for up to 12 weeks of storage or until the product was spoiled. The organism survived but did not grow on summer sausage, grew only slightly on cooked roast beef, grew well on some wiener products but not on others, grew well (10(3) to 10(5) CFU/g increase within 4 weeks) on ham, bologna, and bratwurst, and grew exceptionally well (10(3) to 10(5) CFU/g increase within 4 weeks) on sliced chicken and turkey. The rate of growth depended largely upon the type of product and the pH of the product. Growth was most prolific on processed poultry products. The organism generally grew well on meats near or above pH 6 and poorly or not at all on products near or below pH 5. These results indicate the importance of preventing postprocessing contamination of L. monocytogenes in a variety of ready-to-eat meat products.

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