Superdormant Spores as a Hurdle for Gentle Germination-Inactivation Based Spore Control Strategies

Abstract

Bacterial spore control strategies based on the germination-inactivation principle can lower the thermal load needed to inactivate bacterial spores and thus preserve food quality better. However, the success of this strategy highly depends on the germination of spores, and a subpopulation of spores that fail to germinate or germinate extremely slowly hinders the application of this strategy. This subpopulation of spores is termed ‘superdormant (SD) spores.’ Depending on the source of the germination stimulus, SD spores are categorized as nutrient-SD spores, Ca2+-dipicolinic acid SD spores, dodecylamine-SD spores, and high pressure SD spores. In recent decades, research has been done to isolate these different groups of SD spores and unravel the cause of their germination deficiency as well as their germination capacities. This review summarizes the challenges caused by SD spores, their isolation and characterization, the underlying mechanisms of their germination deficiency, and the future research directions needed to tackle this topic in further depth.

Flow Cytometry Combined With Single Cell Sorting to Study Heterogeneous Germination of Bacillus Spores Under High Pressure

“…However, most of these classical methods have low throughput and the obtained information only reflects the average population under investigation without taking into account heterogeneity within the population. These methods are therefore not ideal for studying heterogeneous spore germination (Reineke et al, 2013b;Zhang and Mathys, 2019). Considering the loss of important information concerning germination heterogeneity in population-level studies, researchers have investigated other techniques to study germination on a single cell level (Margosch et al, 2004;Chen et al, 2006;Zhang et al, 2012;Pandey et al, 2013;van Melis et al, 2014;Trunet et al, 2017).…”

“…A more gentle approach to control spores aims on not directly inactivating the dormant spores but rather using a so called germination-inactivation strategy (Collado et al, 2004;Abee et al, 2011;Lovdal et al, 2011;Zhang and Mathys, 2019). This strategy is based on the well-studied phenomenon that dormant spores lose their resistance after germination, and thus become sensitive toward additional mild decontamination procedures (Collado et al, 2004;Setlow, 2006;Abee et al, 2011;Lovdal et al, 2011).…”

“…Spore germination can be triggered by different stimuli, including nutrients, Ca 2+dipicolinic acid (Ca 2+ -DPA), and isostatic high pressure (HP) (Gould, 1970;Setlow, 2003;Gould, 2006;Baier et al, 2011;Reineke et al, 2013b;Sevenich and Mathys, 2018). From a practical perspective, HP offers clear advantages over other germination-triggering strategies: food products can be treated more homogenously, addition of chemicals like Ca 2+ -DPA are not necessary, and germinated spores and other vegetative cells can be inactivated simultaneously (Gould and Sale, 1970;Knorr et al, 1998;Georget et al, 2014;Doona et al, 2016;Sevenich and Mathys, 2018;Zhang and Mathys, 2019). As a promising nonthermal spore-controlling method, HP also retains food quality better than the state-of-the-art heat sterilization in terms of nutritional value, color and other sensorial attributes (Martinez-Monteagudo et al, 2014;Sevenich and Mathys, 2018).…”

“…Similar to other germination stimuli, HP cannot trigger germination of all spores in a bacterial population. Bacterial spores are notorious for their unpredictable germination responses, resulting in heterogeneous behavior within a population (Setlow, 2003;Luu et al, 2015;Wells-Bennik et al, 2016;Zhang and Mathys, 2019). A fraction of spores, termed superdormant (SD) spores, tend to stay dormant or germinate extremely slowly compared to the rest of the population upon facing germination stimuli (Setlow, 2003;Ghosh and Setlow, 2009;Wells-Bennik et al, 2016).…”

Terminal sterilization of medical devices using vaporized hydrogen peroxide: a review of current methods and emerging opportunities

“…As shown by Humpheson et al (), in their heat challenge of S. enteridis PT4, biphasic inactivation curves were observed at temperatures of 60°C, but these migrated to linear as temperatures were decreased to 51°C. Previous researchers have also reported on the heterogeneity of endospore germination and occurrence of super dormant spores from genetically identical populations that can contribute to delayed germination which can also influence microbial inactivation kinetic models (Hong et al ; Setlow et al ; Zhang and Mathys ). Use of combined analytical techniques, such as FCM, phase contrast, fluorescent and transmission electron microscopy, along with use of Raman spectroscopy will help advance this important field of study.…”