Comparative studies on Salmonella isolations from feeds in ten laboratories.

Pig feed samples, artificially and naturally contaminated with S. typhimurium, were distributed to ten laboratories. The isolation rates obtained by using a standardized pre-enrichment method and the laboratories' "own" methods were compared. In nearly all laboratories the standardized pre-enrichment method gave better results. Extending the duration of incubation of the enrichment medium to 48 h followed by a second subculture improved the isolation rates. In general, a pre-enrichment method should be used for the isolation of salmonellae, especially when they are injured or small numbers of them are expected in the material to be investigated.