[1] MATFORSK - Norwegian Food Res. Inst., Osloveien 1, N-1430 Ås, Norway
[2] Dept. Pharmacol., Microbiol./Food H., Norwegian Coll. of Vet. Medicine, PO Box 8146 Dep., N-0033 Oslo, Norway
[3] Norwegian Meat Cooperative, Dept. of Research and Development, PO Box 360 Økern, N-0513 Oslo, Norway
[4] Roy. Vet. and Agric. University, Dept. of Veterinary Microbiology, Bülowsvej 13, DK-1870 Frederiksberg C, Denmark