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

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. The 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.

[1]  A. Schuchat,et al.  Comparison of cold enrichment and U.S. Department of Agriculture methods for isolating Listeria monocytogenes from naturally contaminated foods. The Listeria Study Group , 1991, Applied and environmental microbiology.

[2]  R. Whittenbury,et al.  Sources of the Lactic Acid Bacteria Occurring in Silage , 1963 .

[3]  D. Fenlon Growth of naturally occurring Listeria spp. in silage: a comparative study of laboratory and farm ensiled grass , 1986 .

[4]  F. Wright,et al.  Characterization by Multilocus Enzyme Electrophoresis of Listeria monocytogenes Isolates Involved in Ovine Listeriosis Outbreaks in Scotland from 1989 to 1991 , 1993, Applied and environmental microbiology.

[5]  P. Boerlin,et al.  Typing of human, animal, food, and environmental isolates of Listeria monocytogenes by multilocus enzyme electrophoresis , 1991, Applied and environmental microbiology.

[6]  C. Nguyen-the,et al.  Factors affecting the growth of Listeria monocytogenes on minimally processed fresh endive. , 1995, The Journal of applied bacteriology.

[7]  L. Mascola,et al.  Epidemic listeriosis associated with Mexican-style cheese. , 1988, The New England journal of medicine.

[8]  D. Fenlon Rapid quantitative assessment of the distribution of Listeria in silage implicated in a suspected outbreak of listeriosis in calves , 1986, Veterinary Record.

[9]  A. Gilmour,et al.  Application of multilocus enzyme electrophoresis and restriction fragment length polymorphism analysis to the typing of Listeria monocytogenes strains isolated from raw milk, nondairy foods, and clinical and veterinary sources , 1994, Applied and environmental microbiology.

[10]  A. Gilmour,et al.  Characterization of Listeria monocytogenes isolated from poultry products and from the poultry-processing environment by random amplification of polymorphic DNA and multilocus enzyme electrophoresis , 1995, Applied and environmental microbiology.

[11]  N. Skovgaard,et al.  Application of multilocus enzyme electrophoresis in studies of the epidemiology of Listeria monocytogenes in Denmark , 1993, Applied and environmental microbiology.

[12]  P. Grimont,et al.  Notes: Listeria ivanovii sp. nov. , 1984 .

[13]  C. Buchrieser,et al.  Investigations related to the epidemic strain involved in the French listeriosis outbreak in 1992 , 1995, Applied and environmental microbiology.

[14]  J. Rocourt,et al.  Différenciation biochimiquedes groupes génomiques de Listeria monocytogenes (sensu lato) , 1983 .

[15]  C. Genigeorgis,et al.  Prevalence of Listeria spp. in Poultry Meat at the Supermarket and Slaughterhouse Level. , 1989, Journal of food protection.

[16]  Karen Sizmur,et al.  LISTERIA IN PREPACKED SALADS , 1988, The Lancet.

[17]  D. Fenlon Wild birds and silage as reservoirs of Listeria in the agricultural environment. , 1985, The Journal of applied bacteriology.

[18]  J. Watkins,et al.  Isolation and enumeration of Listeria monocytogenes from Sewage, Sewage Sludge and River Water. , 1981, The Journal of applied bacteriology.

[19]  A. Hightower,et al.  Epidemic listeriosis--evidence for transmission by food. , 1983, The New England journal of medicine.

[20]  R. J. Gilbert,et al.  The contamination of paté by Listeria monocytogenes in England and Wales in 1989 and 1990 , 1993, Epidemiology and Infection.

[21]  J. Farber,et al.  A Survey of Various Foods for the Presence of Listeria Species. , 1989, Journal of food protection.

[22]  D. Fenlon,et al.  The incidence, numbers and types of Listeria monocytogenes isolated from farm bulk tank milks , 1995, Letters in applied microbiology.

[23]  A. Killinger,et al.  Listeria monocytogenes and listeric infections. , 1966, Bacteriological reviews.