Deactivation of Salmonella Newport in Dairy Manure through Modification of pH and Temperature.

Salmonella enterica serovar Newport (S. Newport) has established a reservoir in dairy cattle.  This pathogenic bacterium can adversely affect animal health and production, and more particularly human health, given the recent high-profile cases of salmonellosis in the US.  We investigated the deactivation of S. Newport in dairy feces in the laboratory under different pH or temperature conditions.  Modification of fecal pH was achieved using aluminum sulfate to the range of pH 3.5 to 5 and with calcium hydroxide to pH 8 to 10.  The fecal samples were inoculated with S. Newport at a target rate of 7 log10 per gram.  Unamended, circumneutral pH manure served as a control.  In a second trial, inoculated dairy feces were incubated at 4, 22 or 37 degrees C.  Lowering the pH of the feces to the range of 3.5 to 4 was highly effective in killing S. Newport, with none detected after day 1.  Increasing pH to near 10 had no effect on Salmonella survival.  However, one-time amendation to adjust fecal pH tended to be short in duration, with the pH approaching that of the unamended control within 3 to 15 days.  Preliminary results suggest that a pH of less than 4 is necessary to suppress or kill inoculated S. Newport.  In the temperature adjustment trials, time to extinction of S. Newport was 14-22 days for the 37 C treatment and 60-64 days for the 22 C treatment.  Incubation at 4 C greatly prolonged S. Newport survival, with a calculated deactivation time of 220 days.  Acidification to pH 4 or below or temperature increase appear to offer the best practical means of reducing S. Newport survival in dairy feces.