The goal of this study is to determine the prevalence of pathogenic Yersinia and Listeria monocytogenes in organic pork production and assess risks in different steps of the pork production chain

Hellström, S.

Korkeala, H.

Laukkanen, R.

Maijala, R.

Nuotio, L.

Ortiz, P.

Ranta, J.

Siekkinen, K.-M.

English

Organic Eprints

Nordic Associationof Agricultural ScientistsNJF Report • Vol. 1 • No 1 • 2005NJF-Seminar 369Organic farming for a new millennium-status and future challengesReport_vol1_no1_2005  02.06.05  10:06  Side 1Published by Nordic Association of Agricultural Scientists (NJF),Section I: Soil, Water and Environment Swedish University of Agricultural Sciences Alnarp, Sweden June 15-17, 2005Electronic version available at www.njf.nuISSN 1653-2015Pathogenic Yersinia and Listeria monocytogenes in organic pork production  R. Laukkanen1, P. Ortiz1, S. Hellström1, K.-M. Siekkinen2, J. Ranta2, L. Nuotio2, R. Maijala1,2 and H. Korkeala1 1University of Helsinki, Faculty of Veterinary Medicine, Department of Food and Environmental Hygiene, P.O. Box 66, FIN-00014 Helsinki University, Finland 2National Veterinary and Food Research Institute EELA, Department of Risk Assessment, P.O. Box 45, FIN-00581 Helsinki, Finland  Abstract  The microbiological safety of organic food has been under some debate, because knowledge of microbial hazards in organic farming, animal production in particular, is scarce. There is some evidence that differences in pig husbandry, farming and production systems can affect the on farm prevalence of foodborne pathogens such as Yersinia and Listeria that can cause serious illness in humans. The goal of this study is to determine the prevalence of pathogenic Yersinia and Listeria monocytogenes in organic pork production and assess risks in different steps of the pork production chain. A total of 1940 faecal, pluck, carcass swab and meat samples were examined for Listeria monocytogenes, Yersinia enterocolitica and Yersinia pseudotuberculosis to assess microbiological safety of organic pork production compared to conventional. Information gained from this study is used to create a more advanced model for the pathogen risks in pork production chain, including special features of organic farming.  Keywords: Listeria monocytogenes, pathogenic Yersinia, pork, prevalence, risk assessment  Introduction  Yersinia enterocolitica, Yersinia pseudotuberculosis and Listeria monocytogenes are foodborne pathogens that can cause serious illness in humans. Yersinia is the third most common enteropathogen reported in humans in Finland, after Campylobacter and Salmonella. In 2003, the number of reported human yersiniosis cases was 647, of which 174 were caused by  Y. pseudotuberculosis and 473 by Y. enterocolitica (Holmström et al, 2003). L. monocytogenes possesses a threat especially for people in high-risk groups such as pregnant women, neonates, immunosuppressed persons and elderly people, but also healthy young people can be infected (Farber & Peterkin, 1991; Miettinen et al, 1999). In 2003, a total of 41 L. monocytogenes cases were reported in Finland, of which over 50% were 65 year-olds or older (Holmström et al, 2003).  Pathogenic Yersinia and L. monocytogenes are commonly found in pig tonsils. In previous papers the prevalence of Y. enterocolitica, Y. pseudotuberculosis and L. monocytogenes in fattening pig tonsils have been 36-65%, 4% and 22%, respectively (Asplund et al, 1990; Fredriksson-Ahomaa et al, 2000; Korte et al, 2002; Niskanen et al, 2002; Autio et al, 2004). Both genera (Yersinia and Listeria) are able to multiply during cold storage and therefore cause a threat in a modern distribution chain of foods.  The microbiological safety of organic food has been under some debate, because knowledge of microbial hazards in organic farming, animal production in particular, is scarce (Bourn & Prescott, 2002). In general, consumers expect the microbiological quality of organic products to be higher compared to that of conventionally grown (Williams & Hammit, 2001). There is 43some evidence that differences in pig husbandry, farming and production systems can affect the prevalence of pathogens such as Yersinia and Listeria. In previous studies the prevalence of L. monocytogenes was found to be higher in pigs raised on silage or wet feed than in pigs fed with dry feed, and lower in specific pathogen free herds (SPF) than non-SPF herds (Skovgaard & Norrung, 1989; Buncic, 1991; Belœil et al, 2003). The prevalence of Y. enterocolitica has been shown to be higher in specialized slaughter pig production than in conventional farrow-to-finish production (Skjerve et al, 1998). It is possible that organic and conventional pig production are similar factors causing differences in microbial status between the two systems.  Risk assessment modelling is a novel tool for decision making in complex systems (Nauta et al, 2000). A quantitative model can pool together large amount of data and provide a simulation framework for different scenarios and control measures. Department of Food and Environmental Hygiene of University of Helsinki and National Veterinary and Food Research Institute have started a research project in co-operation with the Finnish Association for Organic Farming to assess the microbial food safety risks concerning organic versus conventional pork production.  Progress of the project  Altogether 15 farms, 5 organic and 10 conventional, from South-Western Finland were selected for the study. Samples were collected during summer 2003 to winter 2005. In every farm, ca 25 pigs were sampled for L. monocytogenes and pathogenic Yersinia at farm and slaughterhouse. At the farm rectal swabs from pigs and at slaughterhouse samples from intestinal content, pluck, tonsils and carcass were collected. The farm and slaughterhouse samples were taken from the same individuals to allow detailed studies of contamination over production chain. In addition 155 meat samples from meat cutting plants were collected to assess the occurrence of Yersinia and L. monocytogenes in organically and conventionally produced meat. Meat samples were collected from the batches that included sample pigs. The total of 1940 microbiological samples were examined with conventional cultivation methods using modified ISO protocol (1996) for L. monocytogenes, and modified NCFA method (1996) for Yersinia. The remaining analyses of samples should be completed in the summer 2005. In addition, data on possible risk factors were gathered from the farms to assess possible routes of contamination of pigs. Statistic methods will be used to analyse the prevalence data and data on possible risk factors. The information on microbiological tests, on-farm questionnaire and observation results are further used to construct a probability model to describe the probability of infection of L. monocytogenes and pathogenic Yersinia on farm and the transition probability to slaughterhouse. The project should be completed and results reported at the end of the year 2005.  Conclusions  In this project, the information got on the prevalence of L. monocytogenes and pathogenic Yersinia of organic pig farms, contamination routes of the pigs on farm and contamination of the carcasses and meat in food processing can help to evaluate the microbiological safety of organic pork compared to the conventional system. The risk model constructed in this project can be used for the evaluation of the different interventions available for the reduction of the risk for consumers caused by L. monocytogenes, Y. enterocolitica or Y. pseudotuberculosis.  44References  Asplund, K., V. Tuovinen, P. Veijalainen & J. 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(Eds.) The Genus Yersinia. Advances in Experimental Medicine and Biology, 529, 367-369. Miettinen, M.K., A. Siitonen, P. Heiskanen, H. Haajanen, K.J. Björkroth & H.J. Korkeala  (1999). Molecular epidemiology of an outbreak of febrile gastroenteritis caused by Listeria monocytogenes in cold-smoked rainbow trout. Journal of Clinical Microbiology, 37, 2358-60. Nauta, M.J., A.W. van de Giessen & A.M. Henken (2000). A model for evaluating intervention strategies to control Salmonella in the poultry meat production chain. Epidemiology and Infection, 124, 365-373. NCFA (1996). Yersinia enterocolitica. Detection in foods. Nordic Committee on Food Analyisis Method No. 117/1996, 3rd ed, 12pp. Niskanen, T., M. Fredriksson-Ahomaa & H. Korkeala (2002). Yersinia pseudotuberculosis with limited genetic diversity is a common finding in tonsils of fattening pigs. Journal of Food Protection, 57, 540-545. Skjerve, E., B. Lium, B. Nielsen & T. Nesbakken (1998). Control of Yersinia enterocolitica in pigs at herd level. International Journal of Food Microbiology, 45, 195-203. Skovgaard, N. & B. Norrung (1989). The incidence of Listeria spp in faeces of Danish pigs and in minced pork meat. International Journal of Food Microbiology, 8, 59-63. Williams, P.R.D. & J.K. Hammitt (2001). Perceived risks of conventional and organic produce: pesticides, pathogens, and natural toxins. Risk Analysis, 21, 319-330. 45Acknowledgements  This project was funded by Ministry of Agriculture and Forestry, Finland. We thank slaughterhouses, meat cutting plants and farmers for co-operation in this project.  46

Pathogenic Yersinia and Listeria monocytogenes in organic pork production

Pathogenic Yersinia and Listeria monocytogenes in organic pork production

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