ReviewInvestigating germination and outgrowth of bacterial spores at several scales

•Bacterial spore germination and outgrowth is a key issue for food safety and quality.•Germination, outgrowth and growth constitute a complex and heterogeneous process.•This can be examined by various observation and analytical techniques.•These techniques provide information at population or single cell levels.•Combined methods are appropriate to study the behavior of spore-forming bacteria.

BackgroundSpore-forming bacteria are a major cause of food spoilage and food poisoning. Spores that resist physical and chemical treatments used in the food industry may germinate and multiply. Spore germination, outgrowth and growth constitute a complex and highly heterogeneous process.Scope and approachVarious techniques and methods can be used to observe the germination, outgrowth and early multiplication process of spore-forming bacteria and/or to quantify the impact of environmental conditions on its progress over time within a spore population. These techniques can be classified by different criteria: (i) the scale of analysis, from populations or cells to molecules, and (ii) the number of analyzed objects (cells) and (iii) the potential of the method to describe and/or quantify the impact of lethal or sub-lethal treatments or environmental conditions. Such treatments are applied to a spore population or a single spore and take into account parameters at the cellular level (growth capacity, morphological properties) to molecular level (proteomics, transcriptomics, spore molecular composition).Key findings and conclusionA better understanding and quantification of the germination, outgrowth and growth process require the implementation of several complementary methods. Methods providing information at single and population levels, as well as at molecular and cellular levels, are essential to assess and control the fate of spore-forming bacteria development in food systems.