Automated rapid screening of foods for the presence of salmonellae

We previously reported an accelerated method to detect salmonellae in foods . It consisted of a preenrichment step (6 h) followed by immunomagnetic sep aration (IMS) and automated detection, based on positive biochemical charac teristics, during overnight incubation. We describe here a simplified proce dure with a detection limit of 2 CFU/25 g of food, a procedure that does no t require the IMS step. Liquid eggs, milk, ice cream, or poultry were inocu lated with Salmonella or non-Salmonella Enterobacteriaceae organisms (2 to 100 CFU/25 g). Following preenrichment for 6 h at 35 degrees C, samples (3 mi) were added to selective Liquid media (6 ml). Automated Light transmitta nce was recorded during incubation at 42 degrees C in the BioSys instrument . Salmonella-positive samples were identified by a sharp drop in transmitta nce (caused by black discoloration of the media) within 18 h of incubation following the formation of hydrogen sulfide and its reaction with iron ions . Detection of 2 to 10 CFU/25 g of the tested foods was completed in 24 h. A total of 24 Salmonella spp., including heat-injured cells, and 37 non-Sal monella Enterobacteriaceae were tested using the procedure.