Krawczyk Antonina O, de Jong Anne, Omony Jimmy, Holsappel Siger, Wells-Bennik Marjon H J, Kuipers Oscar P, Eijlander Robyn T
Laboratory of Molecular Genetics, University of Groningen, Groningen, the Netherlands.
Top Institute Food and Nutrition (TIFN), Wageningen, the Netherlands.
Appl Environ Microbiol. 2017 Mar 17;83(7). doi: 10.1128/AEM.03122-16. Print 2017 Apr 1.
Spore heat resistance, germination, and outgrowth are problematic bacterial properties compromising food safety and quality. Large interstrain variation in these properties makes prediction and control of spore behavior challenging. High-level heat resistance and slow germination of spores of some natural isolates, encountered in foods, have been attributed to the occurrence of the operon carried on the Tn transposon. In this study, we further investigate the correlation between the presence of this operon in high-level-heat-resistant spores and their germination efficiencies before and after exposure to various sublethal heat treatments (heat activation, or HA), which are known to significantly improve spore responses to nutrient germinants. We show that high-level-heat-resistant spores harboring required higher HA temperatures for efficient germination than spores lacking The optimal spore HA requirements additionally depended on the nutrients used to trigger germination, l-alanine (l-Ala), or a mixture of l-asparagine, d-glucose, d-fructose, and K (AGFK). The distinct HA requirements of these two spore germination pathways are likely related to differences in properties of specific germinant receptors. Moreover, spores that germinated inefficiently in AGFK contained specific changes in sequences of the GerB and GerK germinant receptors, which are involved in this germination response. In contrast, no relation was found between transcription levels of main germination genes and spore germination phenotypes. The findings presented in this study have great implications for practices in the food industry, where heat treatments are commonly used to inactivate pathogenic and spoilage microbes, including bacterial spore formers. This study describes a strong variation in spore germination capacities and requirements for a heat activation treatment, i.e., an exposure to sublethal heat that increases spore responsiveness to nutrient germination triggers, among 17 strains of , including 9 isolates from spoiled food products. Spores of industrial foodborne isolates exhibited, on average, less efficient and slower germination responses and required more severe heat activation than spores from other sources. High heat activation requirements and inefficient, slow germination correlated with elevated resistance of spores to heat and with specific genetic features, indicating a common genetic basis of these three phenotypic traits. Clearly, interstrain variation and numerous factors that shape spore germination behavior challenge standardization of methods to recover highly heat-resistant spores from the environment and have an impact on the efficacy of preservation techniques used by the food industry to control spores.
孢子的耐热性、萌发和生长是影响食品安全和质量的细菌特性问题。这些特性在菌株间存在很大差异，使得对孢子行为的预测和控制具有挑战性。食品中一些天然分离株的孢子具有高水平耐热性和缓慢萌发的特性，这归因于Tn转座子上携带的操纵子的存在。在本研究中，我们进一步研究了这种操纵子在高水平耐热孢子中的存在与它们在暴露于各种亚致死热处理（热激活，或HA）之前和之后的萌发效率之间的相关性，已知这种热处理能显著改善孢子对营养萌发剂的反应。我们发现，携带的高水平耐热孢子比缺乏的孢子在有效萌发时需要更高的HA温度。孢子的最佳HA要求还取决于用于触发萌发的营养物质，即L-丙氨酸（L-Ala），或L-天冬酰胺、D-葡萄糖、D-果糖和K的混合物（AGFK）。这两种孢子萌发途径不同的HA要求可能与特定萌发受体的特性差异有关。此外，在AGFK中萌发效率低下的孢子在参与这种萌发反应的GerB和GerK萌发受体序列中存在特定变化。相反，主要萌发基因的转录水平与孢子萌发表型之间没有关系。本研究的结果对食品工业的实践具有重要意义，在食品工业中，热处理通常用于灭活致病和腐败微生物，包括产芽孢细菌。本研究描述了17株菌（包括9株来自变质食品的分离株）的孢子萌发能力和热激活处理要求（即暴露于亚致死热，以增加孢子对营养萌发触发物的反应）存在很大差异。工业食源性病原体分离株的孢子平均表现出较低的萌发效率和较慢的萌发反应，并且比其他来源的孢子需要更严格的热激活。高热激活要求以及低效、缓慢的萌发与孢子对热的抗性增强以及特定的遗传特征相关，表明这三个表型特征具有共同的遗传基础。显然，菌株间的差异以及影响孢子萌发行为的众多因素对从环境中回收高度耐热孢子的方法标准化提出了挑战，并对食品工业用于控制孢子的保存技术的有效性产生影响。
