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Applied and Environmental Microbiology, March 2006, p. 1833-1842, Vol. 72, No. 3
0099-2240/06/$08.00+0 doi:10.1128/AEM.72.3.1833-1842.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
Survival and Transmission of Salmonella enterica Serovar Typhimurium in an Outdoor Organic Pig Farming Environment
Annette Nygaard Jensen,1* Anders Dalsgaard,2 Anders Stockmarr,1 Eva Møller Nielsen,3 and Dorte Lau Baggesen1Danish Institute for Food and Veterinary Research, Bülowsvej 27, DK-1790 Copenhagen V,1 The Royal Veterinary and Agricultural University, Bülowsvej 17, DK-1870 Frederiksberg C,2 Statens Serum Institut, Artillerivej 5, DK-2300 Copenhagen S, Denmark3
Received 12 October 2005/ Accepted 26 December 2005
It was investigated how organic rearing conditions influence the Salmonella enterica infection dynamics in pigs and whether Salmonella persists in the paddock environment. Pigs inoculated with S. enterica serovar Typhimurium were grouped with Salmonella-negative tracer pigs. Bacteriological and serological testing indicated that organic pigs were susceptible to Salmonella infections, as 26 of 46 (56%) tracer pigs turned culture positive. An intermittent and mainly low-level excretion of Salmonella (<100 cells g–1) partly explains why the bacteriological prevalence appeared lower than the seroprevalence. Salmonella persisted in the paddock environment, as Salmonella was isolated from 46% of soil and water samples (n = 294). After removal of pigs, Salmonella was found in soil samples for up to 5 weeks and in shelter huts during the entire test period (7 weeks). Subsequent introduction of Salmonella-negative pigs into four naturally Salmonella-contaminated paddocks caused Salmonella infections of pigs in two paddocks. In one of these paddocks, all tracer pigs (n = 10) became infected, coinciding with a previous high Salmonella infection rate and high Salmonella excretion level. Our results showed that pigs reared under organic conditions were susceptible to Salmonella infections (just like conventional pigs) and that Salmonella persisting in the paddock environment could pose an infection risk. A driving force for these infections seemed to be pigs with a high Salmonella excretion level, which caused substantial contamination of the environment. This suggests that isolation of animals as soon as a Salmonella infection is indicated by clinical symptoms of diarrhea could be a means of reducing and controlling the spread and persistence of Salmonella in outdoor organic pig production environments.
* Corresponding author. Mailing address: Danish Institute for Food and Veterinary Research, Bülowsvej 27, DK-1790 Copenhagen V, Denmark. Phone: 4572346328. Fax: 4572346001. E-mail: anj{at}dfvf.dk.
Applied and Environmental Microbiology, March 2006, p. 1833-1842, Vol. 72, No. 3
0099-2240/06/$08.00+0 doi:10.1128/AEM.72.3.1833-1842.2006
Copyright © 2006, American Society for Microbiology. All Rights Reserved.
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