Survival of bovine-associated serotypes of Salmonella enterica in bedding sand

Cattle persistently infected with bovine-adapted serotypes of Salmonella enterica are an important animal health and food safety issue. One possible mechanism by which infection is sustained in a dairy herd is by survival of Salmonella in sand used as bedding material. In this study we assessed the survival of 10⁷ to 10⁸ cfu bovine-associated serotypes of Salmonella enterica (sv. Cerro, Dublin, and Heidelberg) in sterile sand, recycled bedding sand, and gray water collected from a Wisconsin dairy farm. All 3 serotypes persisted at relatively high numbers (>10⁶ cfu/g) for at least 28 d in sterile sand, with Salmonella sv. Dublin decreasing less than 1 log₁₀ over 70 d. To our surprise, when low numbers of Salmonella sv. Dublin (10³ cfu) were inoculated into sterile sand, the organism multiplied within 3 d to approximately 10⁶ cfu/g sand and persisted at that level for 28 d. When we inoculated Salmonella sv. Dublin into recycled bedding sand or sand taken directly from cow pens, we observed a significant decrease in colony-forming units by d 7. In contrast, we observed a significant increase in colony-forming units when Salmonella sv. Dublin was inoculated into gray water from the sand recycling system. These data demonstrate that Salmonella can persist for extended periods of time in bedding sand, although this is limited to some extent by the native microbiota in recycled bedding sand.