Dpto. Ingeniería Agronómica, Instituto de Biotecnología Vegetal, Campus de Excelencia Internacional Regional "Campus Mare Nostrum", Escuela Técnica Superior de Ingeniería Agronómica, Universidad Politécnica de Cartagena, Spain.
Tecnología de los Alimentos, Facultad de Veterinaria de Zaragoza, Instituto Agroalimentario de Aragón - IA2 - (Universidad de Zaragoza-CITA), Zaragoza, Spain.
Food Res Int. 2020 Nov;137:109538. doi: 10.1016/j.foodres.2020.109538. Epub 2020 Jul 15.
Heterogeneity in the response of microbial cells to environmental conditions is inherent to every biological system and can be very relevant for food safety, potentially being as important as intrinsic and extrinsic factors. However, previous studies analyzing variability in the microbial response to thermal treatments were limited to data obtained under isothermal conditions, whereas in the reality, environmental conditions are dynamic. In this article we analyse both empirically and through mathematical modelling the variability in the microbial response to thermal treatments under isothermal and dynamic conditions. Heat resistance was studied for four strains of Listeria monocytogenes (Scott A, CECT 4031, CECT 4032 and 12MOB052), in three different matrices (buffered peptone water, pH 7 Mcllvaine buffer and semi-skimmed milk). Under isothermal conditions, between-strain and between-media variability had no impact in the heat resistance, whereas it was very relevant for dynamic conditions. Therefore, the differences observed under dynamic conditions can be attributed to the variability in the ability for developing stress acclimation. The highest acclimation was observed in strain CECT 4031 (10-fold increase of the D-value), while the lowest acclimation was observed in strain CECT 4032 (50% increase of the D-value). Concerning the different media, acclimation was higher in buffered peptone water and semi-skimmed milk than in Mcllvaine buffer of pH 7.0. To the knowledge of the authors, this is the first research work that specifically analyses the variability of microbial adaptation processes that take place under dynamic conditions. It highlights that microbial heat resistance under dynamic conditions are sometimes determined by mechanisms that cannot be observed when cells are treated in isothermal conditions (e.g. acclimation) and can also be affected by variability. Consequently, empirical evidence on variability gathered under isothermal conditions should be extrapolated with care for dynamic conditions.
微生物细胞对外界环境条件的反应的异质性是每个生物系统固有的，这可能对食品安全非常重要，其重要性可能与内在和外在因素相当。然而，之前分析微生物对热处理的反应变异性的研究仅限于在等温条件下获得的数据，而实际上，环境条件是动态的。在本文中，我们通过实验和数学建模分析了在等温和动态条件下微生物对热处理的反应的变异性。研究了四种李斯特菌（斯科特 A、CECT 4031、CECT 4032 和 12MOB052）在三种不同基质（缓冲蛋白胨水、pH7.0 的 Mcllvaine 缓冲液和半脱脂乳）中的耐热性。在等温条件下，菌株间和培养基间的变异性对耐热性没有影响，但对动态条件则非常重要。因此，在动态条件下观察到的差异可归因于适应应激能力的变异性。在 CECT 4031 菌株中观察到最高的适应（D 值增加 10 倍），而在 CECT 4032 菌株中观察到最低的适应（D 值增加 50%）。关于不同的培养基，缓冲蛋白胨水和半脱脂乳中的适应比 pH7.0 的 Mcllvaine 缓冲液中的适应更高。据作者所知，这是首次专门分析在动态条件下发生的微生物适应过程变异性的研究工作。它强调了微生物在动态条件下的耐热性有时是由在等温条件下处理细胞时无法观察到的机制决定的（例如适应），并且还可能受到变异性的影响。因此，在等温条件下收集的关于变异性的经验证据应谨慎外推到动态条件。
