The Growth Characteristics of Heyndrickxia sporothermodurans in Ultra High Temperature (UHT) Milk and Its Inactivation by Commonly Used Sanitation Methods

The presence of Heyndrickxia sporothermodurans is a widespread concern in dairy industry due to its highly thermal-resistant spores. The "Cleaning-in-place" (CIP) system is the primary method used by dairy industry to control them. But the food safety-related properties of H. sporothermodurans remain poorly understood. Thus, this study proposes to determine the growth characteristics and sporulation of H. sporothermodurans in different matrices, as well as the efficacy of various disinfectants against its biofilm and spore. Therefore, the growth of vegetative cell and spore germination in rich media (brain heart infusion, BHI) and ultra-high temperature (UHT) milk for at least 360 h was investigated in this research. In addition, the biofilms of different maturity induced on stainless steel surfaces were sanitized simulating a CIP procedure, using disinfectants (200 mg/mL peracetic acid, 1.5% sodium hydroxide and 1% nitric acid). Scanning electronic microscopy (SEM) was used as a complementary technique to observe the conditioning of the stainless steel surface after 10 d. Subsequently, the effects of these sanitation methods against the spore were performed in 96-well plates. The observation of growth behavior revealed that the vegetative cells and spore cells may be interconverted in a nutrient-rich environment, resulting in a balanced mode in which spores account for approximately 0.1% of the total cells. This could be used to anticipate the number of contaminated bacteria in a UHT plant environment. The sterilization efficiency tests showed that these sanitation methods were efficient against biofilms but not against spores. Therefore, new inactivation strategies against spores should be proposed and should focus on spores adhesion and the biofilms induced by spores.