Abbreviated Preenrichment Period for Recovery of Salmonella spp. from Selected Low-Moisture Dairy Foods

Abstract

A 6-h and a 24-h preenrichment procedure were compared for their ability to recover Salmonella spp. from selected low-moisture dairy foods. The foods were artificially inoculated several days before analysis, and 20 replicate test portions per procedure from each food were examined in each experiment. Samples examined by the 6-h abbreviated procedure were preenriched for 6 h at 35°C in an air incubator or water bath and centrifuged at 4,100 × g for 10 min. Pellets were suspended in tetrathionate broth and incubated for 24 h at 35°C. For the 24-h standard procedure, test portions were preenriched for 24 h at 35°C in an air incubator, subcultured to tetrathionate broth, and incubated for 24 h at 35°C. Selective enrichment broths from both procedures were streaked onto selective agar plates, and presumptive Salmonella isolates were identified by conventional biochemical and serological tests. Recovery of Salmonella spp. from instant nonfat dry milk and dry whole milk was equivalent for both preenrichment procedures. However, the relative effectiveness of the two procedures varied in the recovery of Salmonella spp. from noninstant nonfat dry milk, lactic casein, and rennet casein.