Thermal Inactivation Kinetics of Tulane Virus in Cell-Culture Medium and Spinach.

Abstract

Human noroviruses (HNoVs) cause significant gastrointestinal disease outbreaks worldwide. Tulane virus (TV) is a cultivable HNoV surrogate widely used to determine control measures against HNoVs. The objective of this study was to determine the heat inactivation kinetics (D- and z-values) of TV in cell-culture media and on spiked homogenized spinach using the first-order and Weibull models. TV in cell-culture media at approximately 7 log PFU/mL (PFU-plaque forming unit) in 2-mL glass vials was heated at 52, 54, and56°C for up to 10 min in a circulating water bath. Survivors were enumerated using confluent host LLC-MK2 cells in six-well plates by plaque assay. Data from three replicate treatments assayed in duplicatewere analyzed statistically. D-values by the first-order model for TV in cell-culture media at 52, 54,and 56°C were 4.59±0.05, 2.91±0.05, and 1.74±0.07 min, respectively, with a z-value of 9.09±0.01°C (R2 =0.997). The Weibull model showed td =1 values of 2.53±0.08, 1.99±0.10, and 0.57±0.64 min, respectively, at the same temperatures. The D-values for TV in spinach were 7.94±0.21, 4.09±0.04, and 1.43±0.02 min and the z-value was 10.74±0.01°C (R2 =0.98) by the first-order model and 4.89±0.02, 3.21±0.45, and 0.25±0.38 min for the Weibull model at 50, 54, and 58°C, respectively. In comparison to previously reported results for the cultivable HNoV surrogate, murine norovirus -1, TV in cell-culture media and spiked on spinach homogenates showed lower D- and z-values. TV may not be an ideal HNoV surrogate for heat inactivation studies in cell-culture media or homogenized spinach in vacuum bags.