Matchmaking ranging from glass transition heat, and you can desiccation and heat threshold inside the Salmonella enterica

Relationship anywhere between glass transition temperature, and you can desiccation as well as heat threshold inside the Salmonella enterica

Pathogenic bacteria such as Salmonella enterica exhibit high desiccation tolerance, enabling long-term survival in low water activity (a_w) environments. Although there are many reports on the effects of low a_w on bacterial survival, the mechanism by which bacteria acquire desiccation tolerance and resistance to heat inactivation in low-a_w foods remains unclear. We focused on the glass transition phenomenon, as bacteria may acquire environmental tolerance by state change due to glass transition. In this study, we determined the glass transition temperature (T_g) in S. enterica serovars under different a_w conditions using thermal rheological analysis (TRA). The softening behaviour associated with the state change of bacterial cells was confirmed by TRA, and T_g was determined from the softening behaviour. T_g increased as the a_w ple, while the T_g of five S. enterica serovars was determined as °C to °C at 0.87 a_w, the T_g of all the five serovars increased by °C to °C at 0.43 a_w. Furthermore, to verify the thermal tolerance of bacterial cells, a thermal inactivation assay was conducted at 60°C for 10 min under each a_w condition. A higher survival ratio was observed as a_w decreased; this represented an increase in T_g for Salmonella strains. These results suggest that the glass transition phenomenon of bacterial cells would associate with environmental tolerance.

Citation: Lee K, Shoda M, Kawai K, Koseki S (2020) Relationship anywhere between mug changeover heat, and you may desiccation as well as heat endurance into the Salmonella enterica. PLoS One fifteen(5): e0233638.

Copyright: © 2020 Lee mais aussi al. This is an unbarred access blog post delivered according to the terms of brand new Imaginative Commons Attribution Permit, and this permits unrestricted play with, shipments, and you will breeding in almost any medium, considering the original writer and you will origin try paid.

Funding: This functions christiancafe mobile was supported by this new Japan Area toward Campaign away from Research (JSPS) KAKENHI (Grant JP 18H02148) provided so you’re able to SK. The latest funders had no role when you look at the analysis structure, data range and analysis, decision to publish, otherwise planning of one’s manuscript.

Introduction

Outbreaks of foodborne illnesses caused by dry foods, such as nuts [1–3], chocolate [4–8], cereals , and other foods are continuing worldwide [10–12]. Such foods have low water activity (a_w) and the growth of bacteria causing foodborne illness is not observed. Therefore, microbiological hygiene control has not been regarded as important. However, cases of foodborne illness caused by dry food occur frequently, which means that pathogenic bacteria continue to survive even in a low-a_w environment. Especially, various Salmonella serotypes were found in dry foods associated with outbreaks [1–12]. Indeed, several reports have shown that bacteria causing food poisoning such as enterohemorrhagic Escherichia coli (EHEC) and Salmonella, continue to survive for long periods in a low-a_w environment [13–21]. On the contrary, the rate of bacterial survival decreases under high a_w environments [16,22–24], and it is inferred that a_w and the water content of bacteria have some influence on survival. From these previous studies, we consider that there are some associations between a_w and desiccation tolerance of bacterial cells. However, the mechanism of desiccation tolerance of bacterial cells under low-a_w conditions has not yet been clarified and elucidation of the cause is required.

There is a clue to elucidation of the mechanism of desiccation tolerance in other organisms. For example, extreme environment microorganisms, such as tardigrades and sleeping chironomids that utilize cryptobiosis, are resistant to various external environments such as high temperature, high pressure, as well as dry environments [25–27]. In this study, we assume that bacterial cells would vitrify as well as extreme environmental organisms are considered to acquire environmental stress tolerance. Vitrification of bacterial cells by the glass transition phenomenon might be one of the long-term survival factors in a low-a_w environment. The glass transition phenomenon refers to a state change caused by the increase or decrease in molecular movement in a substance as the temperature and moisture content change [28–30]. The state in which molecular movement is limited, due to the decrease in temperature and a_w, is called a glass state and the substance shows physical properties similar to a solid. Since molecular motion is almost stopped in the glass state, the substance or organism shows high tolerance to various environmental stresses such as heat, desiccation, and pressure. In the present study, we hypothesized that bacterial cells are vitrified in low-a_w environments based on the physicochemical properties of solid particles. In other words, we assumed that bacterial cells enter a glass state due to a decrease in molecular movement accompanying a decrease in a_w, making it difficult for the bacteria to be influenced by external factors. This, in turn, allows for long-term survival, even in a dry environment.