Thermal Resistance of Disease-Associated Salmonella typhimurium in Milk

The thermal resistance of Salmonella typhimurium cultures that had been associated with a major milkborne oubreak of salmonellosis was determined in raw whole milk. Thirteen patient stool isolates and 24 implicated pasteurized milk isolates at concentrations of 1 × 10⁵/ml were screened for heat resistance at 51.8°C. A representative milk strain was heated in replicate at four temperatures from 51.8 to 68.3°C. The z_D value was calculated to be 5.3°C. Mean D-value estimates at 51.8°C were 24.0 and 22.8 min for patient and milk isolates, respectively. Extrapolated D_71.7°C values were 0.24 and 0.22 s, and did not differ significantly (α = 0.05). These isolates would not survive proper pasteurization.