Slow rehydration for detection of Salmonella spp. in feeds and feed ingredients

Rehydration and equilibration (4 h) of feeds and feed ingredients at water/sample ratios (vol/wt) of 1.4 to 3.2 did not markedly increase recovery of Salmonella spp. in the slurry when analyzed by standard cultural and direct enrichment methods. Of 143 naturally contaminated samples examined, equilibration increased levels of detection from 106 to 109 positive samples by the standard cultural method and from 103 to 112 by direct enrichment. Results suggest that nonhomogeneous distribution of low incident numbers of salmonellae in test samples rather than an equilibration-dependent response provided for the observed heterogeneity in recovery patterns. The novel equilibration approach is of limited application and requires validation on an individual food basis.