Comparative and multilaboratory studies of two immunodiffusion method enrichment protocols and the AOAC/Bacteriological Analytical Manual culture method for detection of Salmonella in all foods.

The single enrichment immunodiffusion (1-step), the preenrichment and selective enrichment immunodiffusion (2-step), and the AOAC/Bacteriological Analytical Manual culture methods for Salmonella were evaluated for equivalence in 2 separate studies, a comparative evaluation and a multilaboratory dilution study. In the comparative study, all 3 methods were performed on 10 food types. For 550 samples, analyses resulted in 99.3 and 99.6% agreement between the culture method and the 1-step and 2-step methods, respectively. False negative rates were 0.9 and 0.3% for 1-step and culture, and 0.0% and 0.6% for the 2-step and culture, respectively. Subsequently, 6 food types were included in a multilaboratory dilution-to-extinction study. A sequential dilution series of Salmonella in foods was analyzed by the 3 methods to determine their lower limits of detection for Salmonella. A total of 1185 samples analyzed resulted in 98.9% agreement between 1-step and culture, and 99.7% agreement between 2-step and culture. False negative rates were 1.8 and 0.1% for 1-step and culture, and 0.4 and 0.1% for 2-step and culture, respectively. During these evaluations, 1735 samples and controls representing 10 different naturally contaminated and inoculated foods were tested. The data indicate statistical equivalence of all 3 methods when analyzing all food types.