Matchmaking ranging from glass transition temperatures, and you will desiccation and heat tolerance in Salmonella enterica

03 Aug Matchmaking ranging from glass transition temperatures, and you will desiccation and heat tolerance in Salmonella enterica

Matchmaking ranging from cup transition temperature, and you can desiccation as well as heat tolerance in 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 Yards, Kawai K, Koseki S (2020) Relationship between glass transition temperatures, and you may desiccation and heat tolerance in the Salmonella enterica. PLoS You to fifteen(5): e0233638.

Copyright: © 2020 Lee et al. This really is an open availableness article distributed under the terms of new Creative Commons Attribution Permit, which it permits unrestricted explore, delivery, and you will reproduction in virtually any average, considering the original copywriter and you will supply is paid.

Funding: It work is backed by the fresh new The japanese Society into Strategy out-of Technology (JSPS) KAKENHI (Give JP 18H02148) offered in order to SK. Brand new funders didn’t come with part in the research structure, investigation range and you may data, decision to post, otherwise thinking of manuscript.

Addition

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.