The incidence and level of Listeria monocytogenes contamination of food sources at primary production and initial processing

Abstract

1996. Listeria monocytogenes was isolated in low numbers from a variety of environmental samples associated with the primary production of food, including vegetation, faeces and meat. T h e organism was rarely detected on growing grass and vegetables prior to processing. The excretion of L. monocytogenes by farm animals was linked to their diet, with animals fed entirely on hay or manufactured diets not excreting detectable levels of Listeria (i.e. absence in 25 g). However, animals fed on silage, which is frequently contaminated with L. monocytogenes, commonly excreted the organism. Transport of live animals over long distances ( > 100 km) significantly increased the level of excretion of Listeria, but the contamination of carcasses of sheep and cattle was not high. Pigs and poultry faeces were free of Listeria prior to slaughter and pig carcasses were not found to have Listeria present. Frozen and chilled chicken did show detectable levels reflecting the greater potential for contamination during poultry processing. Samples of minced beef were tested and 21 of 23 samples were positive for L. monocytogenes, demonstrating that processing significantly increases the level of contamination compared to whole carcasses. Multilocus enzyme electrophoresis of a representative selection of the isolates showed that there was a wide range of electrophoretic types present in the primary production environment, relatively few of which have been linked to cases of human listeriosis. However, these types do arise on farms and occasional contamination of food raw material by potentially virulent strains may be sufficient to allow adaptable strains to become established in the processing environment and thus be responsible for more widespread contamination of the food available to the consumer.

Isolation and characterization of Listeria monocytogenes and other Listeria species in foods of animal origin in Addis Ababa, Ethiopia

“…L. monocytogenes is an intracellular Grampositive non-sporulating pathogenic bacterium with wide spread presence in nature, affecting a wide range of domestic and wild animals and humans [6]. In the vast majority of human cases, infection is the result of consumption of contaminated food [7]. Although the infectious dose remains unknown and is most likely host dependent, the resulting invasive disease, listeriosis, is a serious illness with a high fatality rate [8].…”

Incidence of Listeria monocytogenes and Escherichia coli O157:H7 in two Kasar Cheese processing environments

“…However, post-processing contamination of product with strains associated with the processing environment can occur (Harvey & Gilmour, 1993). Furthermore, various studies have indicated that certain strains of L. monocytogenes survive within the food processing environment (Fenlon, 1996;Nørrung & Skovgaard, 1993;Senczek, Stephan, & Untermann, 2000;Unnerstad et al, 1996) and the persistence of such strains in a food processing plant is of particular concern as they have the potential to act as a continual source of contamination of the processed product (Sashara & Zottola, 1993).…”

Survey of Listeria monocytogenes in ready-to-eat products: Prevalence by brands and retail establishments for exposure assessment of listeriosis in Northern Spain

“…Listeria monocytogenes is a food-borne pathogen widely distributed throughout the natural environment (Fenlon, Wilson, & Donachie, 1996) and consequently, it is present in many animal and plant food products. Its extended distribution throughout the environment and the psychrotrophic character of the pathogen, appear to be the main causes of its high prevalence in different kinds of refrigerated ready-to-eat products (RTE) (Lianou & Sofos, 2007).…”