Improved Temperature-Gradient Incubator and the Maximal Growth Temperature and Heat Resistance of Salmonella

An improved all-metal temperature-gradient incubator produces its gradient by means of a bar permanently installed in a near-vertical position with its lower end in a cool constant-temperature water bath and with thermostatically controlled heaters near its top. Bolts hold the incubator in contact with the temperature-gradient bar, and polyurethane foam insulates the entire assemblage during use. Maximal growth temperatures of 34 representative strains ofSalmonella were found to be between 43.2 and 46.2 C. In an agar medium with an initial level of 106 cells per milliliter, no strain survived 50 C for 48 hr.S. senftenberg 775W showed no greater heat resistance at or near 48 C than did other species or otherS. senftenberg strains. However, it was considerably more resistant than other strains at 55 C.