Short-time thermal inactivation of surrogates of the public transport microbiome with a low-cost thermoresistometer

Abstract

In this study, the thermal inactivation of the bacterial genera Staphylococcus, Enterococcus and Burkholderia, which can be found in public transportation environments, as well as the bacteriophage MS2 as a surrogate for potential viral pathogens are investigated. To quantify the thermal inactivation characteristic, an automated and inexpensive thermoresistometer is constructed and set up, which enables the microorganisms to be exposed to short-term thermal shocks. The time dependent temperature curves were measured to account for heat-up and cooling times. Afterwards, the microorganisms were exposed to temperatures in the range of 50 °C to 85 °C for durations of 2 s up to 10 s and the thermal inactivation of the respective microorganisms was measured by counting colony forming units (CFU) and plague forming units (PFU). The data was visualized and fitted to an analytical thermodynamic model based on a first-order reaction and the Arrhenius equation to predict thermal inactivation times. This study reports the first measured thermal inactivation values for E. viikkiensis and B. lata, which have not been studied before. The results for MS2 and S. capitis show significantly shorter inactivation times than previous experiments. After exposure to 85 °C for 2 s there was no measurable survival of all tested microorganisms. The semi-automated test setup used allows for consistent measurements and can be adapted by other research groups.