Seasonal incidence and molecular characterization of Salmonella from dairy cows, calves, and farm environment.

The occurrence patterns and molecular characteristics of Salmonella are important for surveillance and control of the pathogens. Objectives of this study were to determine month-to-month variation and seasonal effects on the occurrence of Salmonella in dairy animals and environments and to characterize selected Salmonella isolates. A total of 7680 animal and environmental samples, collected monthly from a dairy farm, were analyzed for the presence of Salmonella during a 12-month study. Major sources of Salmonella on the dairy farm (% positive) were milking parlor air (62%) and bird droppings (63%) during winter; feeds (50-58%), water (53-67%), calf bedding (63%), soils (60-63%), milking parlor air (60%), and bird droppings (50%) in spring; all animal and environmental samples (40-92%) except milking parlor air (25%) and bulk tank milk (29%) in summer; and feeds (60-71%), cow beddings (59%), cow soils (50%), air (46-71%), and insects (63%) during fall. Salmonella ribotyping indicated that most serovars came from different sources but some might have originated from a common source and transmitted from site to site on the farm. These data provide some important information on key animal and environmental sampling sites needed to initiate on-farm management programs for control of this important foodborne pathogen.

Evaluation of methods for recovery of Salmonella from dairy cattle, poultry, and swine farms.

Current official methods for detection and isolation of Salmonella are mostly designed for foods. The objective of this study was to determine optimal methods for detection and isolation of Salmonella from animal and environmental samples of dairy, poultry, and swine farms. Preenrichment in lactose broth versus direct enrichment (no preenrichment) prior to selective enrichment in Rappaport-Vassiliadis, selenite cystine, and tetrathionate incubated at 35 and 42 degrees C and in four differential/selective plating media (brilliant green, bismuth sulfite, Hektoen enteric, and xylose-lysine-tergitol 4 agar base) were evaluated for their ability to recover Salmonella from artificially contaminated samples. The effects of pH adjustments to samples on Salmonella recovery were determined. A pH adjustment of the enrichment broth to 6.8 +/- 0.2 after addition of samples significantly improved recovery of Salmonella. The most effective medium combinations for isolation of Salmonella from farm samples depended on the type of samples. Generalizations of protocols for recovery of Salmonella from farm samples might result in poor recovery, increased recovery time, and increased sample processing costs.