Surviving spores can germinate and resume vegetative growth in a food product and subsequently cause spoilage ( 1, 5, 6). Because of their resistance to environmental stresses, such as extreme temperatures, desiccation, radiation, and exposure to different chemicals, spores are able to survive preservation treatments that are applied in the food industry ( 2, – 4). 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.īacillus subtilis spores, which are widely present in nature, can easily contaminate food products ( 1, 2).
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.
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. subtilis, including 9 isolates from spoiled food products. IMPORTANCE 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 B. 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. In contrast, no relation was found between transcription levels of main germination genes and spore germination phenotypes. 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. The distinct HA requirements of these two spore germination pathways are likely related to differences in properties of specific germinant receptors. 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). We show that high-level-heat-resistant spores harboring spoVA 2mob required higher HA temperatures for efficient germination than spores lacking spoVA 2mob. 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.
High-level heat resistance and slow germination of spores of some natural Bacillus subtilis isolates, encountered in foods, have been attributed to the occurrence of the spoVA 2mob operon carried on the Tn 1546 transposon. Large interstrain variation in these properties makes prediction and control of spore behavior challenging. Spore heat resistance, germination, and outgrowth are problematic bacterial properties compromising food safety and quality.
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