Survival characteristics of Salmonella enterica serovar Newport in the dairy farm environment

Multi-drug resistant (MDR) Salmonella enterica serovar Newport (S. Newport) has established a reservoir in dairy cattle. Infected herds suffer significant mortality in both adult and young animals, posing a considerable economic loss to producers. Land application of manure from infected animals may further spread the pathogen into the agroecosystem, causing public health concerns. Previous work by our group demonstrated that the organism persisted in manure and manured soil for 6 to 10 mo under laboratory conditions. In the present study, we determined the survival characteristics of MDR S. Newport in a dairy lagoon, compost pile, and soil of a grass field under natural conditions using environmental sentinel chambers with an initial concentration of S. Newport around 7 log₁₀ per gram. In the static compost pile at 64°C, S. Newport was eliminated within 18 h. In the dairy effluent lagoon, the pathogen survived for >137 d, whereas in the field soil, the organisms persisted for over 276 d. The survival of MDR S. Newport in both the lagoon and field soil followed a pattern of (1) an increase or plateau for a few days, (2) log-linear decline for 6 to 13 wk, and (3) a long tailing phase at low and variable concentration for 4 to 9 mo. Log reduction times (days required for 90% decrease in concentration) based on the log-linear decline phase were 7 d in the lagoon and 14 to 20 d in the soil. Conditions leading to faster inactivation during the initial phase do not necessarily translate into a quicker elimination of the pathogen. Regression models of the log-linear phase may be inaccurate for estimating complete pathogen elimination.