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

Abstract

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.

Implementation and effectiveness of the HACCP and pre-requisites in food establishments

“…The prevalence in grilled samples is associated with inadequate heat treatment (Passos & Kuay, 2002), while the prevalence in meat that was cooked with sauce, whose cooking time is greater, is associated with poor maintenance or inadequate reheating. Fenlon et al, 1996, observed that the prevalence of Listeria spp. in meat and meat products may be attributed either to improper hygienic practice during processing or to food handlers.…”

Listeria monocytogenes contamination of finishing pigs: an exploratory epidemiological survey in France

“…In the literature, the detection of the L. monocytogenes pig batch status has been more frequently described by means of samples taken at the slaughterhouse. Sampling methods were either individual coprology [1,14,40,42], tonsillar swabbing [26] or skin swabbing [11] on a sample of pigs. The ability of the skin swabbing method to detect L. monocytogenes contamination of pigs has already been demonstrated [11].…”

“…It was early suspected that growing pigs were resistant to L. monocytogenes infection [6]. Since then several reports have mentioned that L. monocytogenes is asymptomatically carried by the pigs [1,5,14,23,26,40,43].…”

Gamma Irradiation for Fresh Produce

“…Similarly, the application of raw animal manure for fertilizer increases the threat of contamination on fruits and vegetables ( Brackett, 1992). Direct or indirect pathogen contamination of fresh produce can occur at many points in the production chain during growth and processing (Fenlon, et al, 1996; Beuchat and Ryu. 1997), thus presenting a food safety challenge to consumers.…”