Heat Inactivation Kinetics of Staphylococcus carnosus Chr CS-299 a Potential Surrogate for Hepatitis A Virus

Introduction: Thermal treatment is a common method for inactivating microbial pathogens in a wide range of food products. Recent studies have shown that hepatitis A virus (HAV) has a D_72°C of 0.9 min in buffer which is greater than vegetative bacterial pathogens. Common surrogates, such as Listeria innocua, are not resistant enough to be used as surrogates for HAV and thus, new surrogates need to be identified.

Purpose: The purpose of this study was to compare the thermal inactivation kinetics (D- and z-values) of Staphylococcus carnosus at different incubation temperatures to identify a potential surrogate for HAV.

Methods: Thermal inactivation of S. carnosus Chr CS-299 was performed in phosphate buffered saline (PBS) following incubation at 32°C or 48°C. A total of 7.6 log CFU/ml of S. carnosus in PBS was added to 2 ml vials. Thermal inactivation studies were performed at 65, 67, and 70°C. Vials were removed at various time points, cooled in an ice bath, plated on BHI agar and incubated for 72 h at 32°C or 48°C. Each trial was conducted in duplicate and replicated three times. D- and z-values were determined using a first-order model.

Results: For 32°C incubation, D-values for S. carnosus in PBS were 1.59 ± 0.2, 0.91 ± 0.1 and 0.34 ± 0.05 min, at 65, 67, and 70°C, respectively, with a z-value of 7.46°C. For 48°C incubation, D-values were 3.4 ± 0.16, 1.43 ± 0.01 and 0.48 ± 0.03 min, at the same respective temperatures, with a z-value of 5.93°C. Thus, using 48°C incubation, S. carnosus could be a potential surrogate for HAV (D_72°C= 0.9 min).

Significance: Based on inactivation kinetics, ease of incubation, and non-pathogenicity, S. carnosus could be used for validation studies of HAV. Additionally, it was shown that a significant increase in heat resistance could be achieved by increasing the incubation temperature.