Timed-release capsule method for the detection of salmonellae in foods and feeds

A new method was developed for the detection of injured and uninjured salmonellae in foods and feeds. The steps of pre-enrichment in a nonselective broth and selective enrichment in a selective medium were combined into a single procedure. This was achieved by the gradual release of selective agents from wax-coated gelatin capsules added at the time of inoculation of nonselective basal broths. Pre-enrichment in lactose broth was combined with selective enrichment in tetrathionate or selenite-cystine broth by using timed-release capsules containing iodine or selenite. Five different categories of foods and feeds, naturally contaminated with salmonellae, were examined to compare the efficiencies of the capsule methods with conventional procedures. Combination of the separate steps of pre-enrichment and selective enrichment into a single procedure was feasible and resulted in substantial savings of labor and materials.