Superdormant spores of Bacillus species have elevated wet-heat resistance and temperature requirements for heat activation

Characterization of high-pressure-treated Bacillus subtilis spore populations using flow cytometry - Shedding light on spore superdormancy at 550 MPa

Mild spore inactivation can be challenging in industry because of the remarkable resistance of bacterial spores. High pressure (HP) can trigger spore germination, which reduces the spore's resistance, and thereby allows mild spore inactivation. However, spore germination is heterogenous. Some slowly germinating or non-germinating spores called superdormant spores remain resistant and can survive. Therefore, superdormant spores need to be characterized to understand the causes of their germination deficiency. Bacillus subtilis spores were pressurized for 50 s - 6 min at a very high pressure (vHP) level of 550 MPa and 60 °C in buffer to trigger germination. For a rapid quantification of the remaining ungerminated superdormant spores, flow cytometry (FCM) analysis was validated using single cell sorting and growth analysis. FCM based on propidium iodide (PI) and SYTO16 can be used for 550 MPa-superdormant spores after short vHP treatments of ≤1 min and post-HP incubation at 37 °C or 60 °C. The need for a post-HP incubation is particular for vHP treatments. The incubation was successful to separate FCM signals from superdormant and germinated spores, thus allowing superdormant spore quantification. The SYTO16 and PI fluorescence levels did not necessarily indicate superdormancy or apparent viability. This highlights the general need for FCM validation for different HP treatment conditions. The ∼7 % of ungerminated, i.e., superdormant, spores were isolated after a vHP treatment (550 MPa, 60 °C, 43-52 s). This allowed the characterization of vHP superdormant spores for the first time. The superdormant spores had a similar dipicolinic acid content as spores of the initial dormant population. Descendants of superdormant spores had a normal vHP germination capacity. The causes of vHP superdormancy were thus unlikely linked to the dipicolinic acid content or a permanent genetic change. Isolated superdormant spores germinated better in a second vHP treatment compared to the initial spore population. This has not been observed for other germination stimuli so far. In addition, the germination capacity of the initial spore population was time-dependent. A vHP germination deficiency can therefore be lost over time and seems to be caused by transient factors. Permanent cellular properties played a minor role as causes of superdormancy under chosen HP treatment conditions. The study gained new fundamental insights in vHP superdormancy which are of applied interest. Understanding superdormancy helps to efficiently develop a strategy to avoid superdormant spores and hence to inactivate all spores. The development of a mild HP spore germination-inactivation process aims at better preserving the food quality.

Characterization, whole-genome sequence analysis, and protease production of a new thermophilic Bacillus licheniformis strain isolated from Debagh hot spring, Algeria

A new thermophilic strain, designated as Bacillus sp. LMB3902, was isolated from Hammam Debagh, the hottest spring in Algeria (up to 98 °C). This isolate showed high protease production in skim milk media at 55 °C and exhibited significant specific protease activity by using azocasein as a substrate (157.50 U/mg). Through conventional methods, chemotaxonomic characteristics, 16S rRNA gene sequencing, and comparative genomic analysis with the closely related strain Bacillus licheniformis DSM 13 (ATCC 14580 T), the isolate Bacillus sp. LMB3902 was identified as a potentially new strain of Bacillus licheniformis. In addition, the gene functions of Bacillus sp. LMB3902 strain were predicted using the Gene Ontology, Kyoto Encyclopedia of Genes and Genomes, Clusters of Orthologous Groups, Non-Redundant Protein Sequence Database, Swiss-Prot, and Pfam databases. The results showed that the genome size of Bacillus sp. LMB3902 was 4.279.557 bp, with an average GC content of 46%. The genome contained 4.760 predicted genes, including 8 rRNAs, 78 tRNAs, and 24 sRNAs. A total of 235 protease genes were annotated including 50 proteases with transmembrane helix structures and eight secreted proteases with signal peptides. Additionally, the majority of secondary metabolites found by antiSMASH platform showed low similarity to identified natural products, such as fengicin (53%), lichenysin (57%), and surfactin (34%), suggesting that this strain may encode for novel uncharacterized natural products which can be useful for biotechnological applications. This study is the first report that describes the complete genome sequence, taxono-genomics, and gene annotation as well as protease production of the Bacillus genus in this hydrothermal vent.

Clostridioides difficile Biofilm

Clostridioides difficile infection (CDI), previously Clostridium difficile infection, is a symptomatic infection of the large intestine caused by the spore-forming anaerobic, gram-positive bacterium Clostridioides difficile. CDI is an important healthcare-associated disease worldwide, characterized by high levels of recurrence, morbidity, and mortality. CDI is observed at a higher rate in immunocompromised patients after antimicrobial therapy, with antibiotics disrupting the commensal microbiota and promoting C. difficile colonization of the gastrointestinal tract.A rise in clinical isolates resistant to multiple antibiotics and the reduced susceptibility to the most commonly used antibiotic molecules have made the treatment of CDI more complicated, allowing the persistence of C. difficile in the intestinal environment.Gut colonization and biofilm formation have been suggested to contribute to the pathogenesis and persistence of C. difficile. In fact, biofilm growth is considered as a serious threat because of the related antimicrobial tolerance that makes antibiotic therapy often ineffective. This is the reason why the involvement of C. difficile biofilm in the pathogenesis and recurrence of CDI is attracting more and more interest, and the mechanisms underlying biofilm formation of C. difficile as well as the role of biofilm in CDI are increasingly being studied by researchers in the field.Findings on C. difficile biofilm, possible implications in CDI pathogenesis and treatment, efficacy of currently available antibiotics in treating biofilm-forming C. difficile strains, and some antimicrobial alternatives under investigation will be discussed here.

Dynamic Changes in the Microbial Community and Metabolite Profile during the Pile Fermentation Process of Fuzhuan Brick Tea

The pile fermentation process of Fuzhuan brick tea is unique in that it involves preheating without the use of starter cultures. The detailed metabolite changes and their drivers during this procedure are not known. Characterizing these unknown changes that occur in the metabolites and microbes during pile fermentation of Fuzhuan brick tea is important for industrial modernization of this traditional fermented food. Using microbial DNA amplicon sequencing, mass spectrometry-based untargeted metabolomics, and feature-based molecular networking, we herein reveal that significant changes in the microbial community occur before changes in the metabolite profile. These changes were characterized by a decrease in Klebsiella and Aspergillus, alongside an increase in Bacillus and Eurotium. The decrease in lysophosphatidylcholines, unsaturated fatty acids, and some astringent flavan-3-ols and bitter amino acids, as well as the increase in some less astringent flavan-3-ols and sweet or umami amino acids, contributed importantly to the overall changes observed in the metabolite profile. The majority of these changes was caused by bacterial metabolism and the corresponding heat generated by it.

Spatial and temporal dynamics of the bacterial community under experimental warming in field-grown wheat

Climate change may lead to adverse effects on agricultural crops, plant microbiomes have the potential to help hosts counteract these effects. While plant-microbe interactions are known to be sensitive to temperature, how warming affects the community composition and functioning of plant microbiomes in most agricultural crops is still unclear. Here, we utilized a 10-year field experiment to investigate the effects of warming on root zone carbon availability, microbial activity and community composition at spatial (root, rhizosphere and bulk soil) and temporal (tillering, jointing and ripening stages of plants) scales in field-grown wheat (Triticum aestivum L.). The dissolved organic carbon and microbial activity in the rhizosphere were increased by soil warming and varied considerably across wheat growth stages. Warming exerted stronger effects on the microbial community composition in the root and rhizosphere samples than in the bulk soil. Microbial community composition, particularly the phyla Actinobacteria and Firmicutes, shifted considerably in response to warming. Interestingly, the abundance of a number of known copiotrophic taxa, such as Pseudomonas and Bacillus, and genera in Actinomycetales increased in the roots and rhizosphere under warming and the increase in these taxa implies that they may play a role in increasing the resilience of plants to warming. Taken together, we demonstrated that soil warming along with root proximity and plant growth status drives changes in the microbial community composition and function in the wheat root zone.

Characterization of the Culturable Sporobiota of Spanish Olive Groves and Its Tolerance toward Environmental Challenges

Olive agriculture presents an integral economic and social pillar of the Mediterranean region with 95% of the world's olive tree population concentrated in this area. A diverse ecosystem consisting of fungi, archaea, viruses, protozoa, and microbial communities-the soil microbiome-plays a central role in maintaining healthy soils while keeping up productivity. Spore-forming organisms (i.e., the sporobiota) have been identified as one of the predominant communities of the soil microbiome and are known for the wide variety of antimicrobial properties and extraordinary resistance. Hence, the aim of this work was to determine the culturable sporobiota of Spanish olive orchards and characterize its phenotypic properties toward common environmental challenges. A collection of 417 heat-resistant bacteria were isolated from five Spanish olive orchards. This collective was termed the "olive sporobiota." Rep-PCR clustering of representative isolates revealed that they all belonged to the group of Bacillus spp., or closely related species, showing a great variety of species and strains. Representative isolates showed susceptibility to common antibiotics, as well as good resistance to heavy metal exposure, with an order of metal tolerance determined as iron > copper > nickel > manganese > zinc > cadmium. Finally, we showed that the application of mineral fertilizer can in several cases enhance bacterial growth and thus potentially increase the relative proportion of the sporobiota in the olive grove ecosystem. In summary, the identification of the culturable olive sporobiota increases our understanding of the microbial diversity in Spanish olive groves, while tolerance and resistance profiles provide important insights into the phenotypic characteristics of the microbial community. IMPORTANCE Microbial communities are a key component of healthy soils. Spore-forming microorganisms represent a large fraction of this community-termed the "sporobiota"-and play a central role in creating a conducive environment for plant growth and food production. In addition, given their unique features, such as extraordinary stability and antimicrobial properties, members of the sporobiota present interesting candidates for biotechnological applications, such as sustainable plant protection products or in a clinical setting. For this, however, more information is needed on the spore-forming community of agricultural installations, ultimately promoting a transition toward a more sustainable agriculture.

Identification and characterization of new proteins crucial for bacterial spore resistance and germination

2Duf, named after the presence of a transmembrane (TM) Duf421 domain and a small Duf1657 domain in its sequence, is likely located in the inner membrane (IM) of spores in some Bacillus species carrying a transposon with an operon termed spoVA ^2mob. These spores are known for their extreme resistance to wet heat, and 2Duf is believed to be the primary contributor to this trait. In this study, we found that the absence of YetF or YdfS, both Duf421 domain-containing proteins and found only in wild-type (wt) B. subtilis spores with YetF more abundant, leads to decreased resistance to wet heat and agents that can damage spore core components. The IM phospholipid compositions and core water and calcium-dipicolinic acid levels of YetF-deficient spores are similar to those of wt spores, but the deficiency could be restored by ectopic insertion of yetF, and overexpression of YetF increased wt spore resistance to wet heat. In addition, yetF and ydfS spores have decreased germination rates as individuals and populations with germinant receptor-dependent germinants and increased sensitivity to wet heat during germination, potentially due to damage to IM proteins. These data are consistent with a model in which YetF, YdfS and their homologs modify IM structure to reduce IM permeability and stabilize IM proteins against wet heat damage. Multiple yetF homologs are also present in other spore forming Bacilli and Clostridia, and even some asporogenous Firmicutes, but fewer in asporogenous species. The crystal structure of a YetF tetramer lacking the TM helices has been reported and features two distinct globular subdomains in each monomer. Sequence alignment and structure prediction suggest this fold is likely shared by other Duf421-containing proteins, including 2Duf. We have also identified naturally occurring 2duf homologs in some Bacilli and Clostridia species and in wt Bacillus cereus spores, but not in wt B. subtilis. Notably, the genomic organization around the 2duf gene in most of these species is similar to that in spoVA ^2mob, suggesting that one of these species was the source of the genes on this operon in the extremely wet heat resistant spore formers.

A Comprehensive Review of Variability in the Thermal Resistance (D-Values) of Food-Borne Pathogens-A Challenge for Thermal Validation Trials

The thermal processing of food relies heavily on determining the right time and temperature regime required to inactivate bacterial contaminants to an acceptable limit. To design a thermal processing regime with an accurate time and temperature combination, the D-values of targeted microorganisms are either referred to or estimated. The D-value is the time required at a given temperature to reduce the bacterial population by 90%. The D-value can vary depending on various factors such as the food matrix, the bacterial strain, and the conditions it has previously been exposed to; the intrinsic properties of the food (moisture, water activity, fat content, and pH); the method used to expose the microorganism to the thermal treatment either at the laboratory or commercial scale; the approach used to estimate the number of survivors; and the statistical model used for the analysis of the data. This review focused on Bacillus cereus, Cronobacter sakazakii, Escherichia coli, Listeria monocytogenes, and Clostridium perfringens owing to their pathogenicity and the availability of publications on their thermal resistance. The literature indicates a significant variation in D-values reported for the same strain, and it is concluded that when designing thermal processing regimes, the impact of multiple factors on the D-values of a specific microorganism needs to be considered. Further, owing to the complexity of the interactions involved, the effectiveness of regimes derived laboratory data must be confirmed within industrial food processing settings.

Heat activation and inactivation of bacterial spores. Is there an overlap?

Heat activation at a sublethal temperature is widely applied to promote Bacillus species spore germination. This treatment also has potential to be employed in food processing to eliminate undesired bacterial spores by enhancing their germination, and then inactivating the less heat resistant germinated spores at a milder temperature. However, incorrect heat treatment could also generate heat damage in spores, and lead to more heterogeneous spore germination. Here, the heat activation and heat damage profile of Bacillus subtilis spores was determined by testing spore germination and outgrowth at both population and single spore levels. The heat treatments used were 40-80°C, and for 0-300 min. The results were as follows. 1) Heat activation at 40-70°C promoted L-valine and L-asparagine-glucose-fructose-potassium (AGFK) induced germination in a time dependent manner. 2) The optimal heat activation temperatures for AGFK and L-valine germination via the GerB plus GerK or GerA germinant receptors were 65 and 50-65°C, respectively. 3) Heat inactivation of dormant spores appeared at 70°C, and the heat damage of molecules essential for germination and growth began at 70 and 65°C, respectively. 4) Heat treatment at 75°C resulted in both activation of germination and damage to the germination apparatus, and 80°C treatment caused more pronounced heat damage. 5) For the spores that should withstand adverse environmental temperatures in nature, heat activation seems functional for a subsequent optimal germination process, while heat damage affected both germination and outgrowth. Importance Bacterial spores are thermal resistant structures that can thus survive preservation strategies and revive through the process of spore germination. The more heat resistant spores are the more heterogeneous they germinate upon adding germinants. Upon germination spores can cause food spoilage and cause food intoxication. Here we provide new information on both heat activation and inactivation regimes and their effects on the (heterogeneity of) spore germination.

Moderate high-pressure superdormancy in Bacillus spores: properties of superdormant spores and proteins potentially influencing moderate high-pressure germination

Resistant bacterial spores are a major concern in industrial decontamination processes. An approach known as pressure-mediated germination-inactivation strategy aims to artificially germinate spores by isostatic pressure to mitigate their resistance to inactivation processes. The successful implementation of such a germination-inactivation strategy relies on the germination of all spores. However, germination is heterogeneous, with some “superdormant” spores germinating extremely slowly or not at all. The present study investigated potential underlying reasons for moderate high-pressure (150 MPa; 37°C) superdormancy of Bacillus subtilis spores. The water and dipicolinic acid content of superdormant spores was compared with that of the initial dormant spore population. The results suggest that water and dipicolinic acid content are not major drivers of moderate high-pressure superdormancy. A proteomic analysis was used to identify proteins that were quantified at significantly different levels in superdormant spores. Subsequent validation of the germination capacity of deletion mutants revealed that the presence of protein YhcN is required for efficient moderate high-pressure germination and that proteins MinC, cse60, and SspK may also play a role, albeit a minor one.

IMPORTANCE Spore-forming bacteria are ubiquitous in nature and, as a consequence, inevitably enter the food chain or other processing environments. Their presence can lead to significant spoilage or safety-related issues. Intensive treatment is usually required to inactivate them; however, this treatment harms important product quality attributes. A pressure-mediated germination-inactivation approach can balance the need for effective spore inactivation and retention of sensitive ingredients. However, superdormant spores are the bottleneck preventing the successful and safe implementation of such a strategy. An in-depth understanding of moderate high-pressure germination and the underlying causes of superdormancy is necessary to advance the development of mild high pressure-based spore control technologies. The approach used in this work allowed the identification of proteins that have not yet been associated with reduced germination at moderate high pressure. This research paves the way for further studies on the germination and superdormancy mechanisms in spores, assisting the development of mild spore inactivation strategies.

The effect of high pressure combined with moderate temperature and peptidoglycan fragments on spore inactivation

High pressure processing (HPP) is a promising non-thermal processing method for food production. However, extremely high pressure and temperature are often required to achieve spores inactivation and commercial sterilization using HPP. In this study, the combined treatment of HPP, moderate temperature, and peptidoglycan fragments (PGF) for spore inactivation was investigated. The combined treatment of 200 MPa and 1 mg/mL PGF at 80 °C for 20 min resulted in 8.6 log inactivation of Bacillus subtilis 168 and more than 5 log reductions of Clostridium sporogenes PA3679 spores, respectively. A strong synergistic effect on spore inactivation among HPP, PGF, and temperature was observed. By comparing the effect of the treatment on the fluidity of the inner membrane and structural change of spores using fluorescence assay, a probable inactivation mechanism was proposed. It was concluded that the spores were firstly triggered to enter the Stage I of the germination process by HPP and PGF, and then immediately inactivated by the mild heat. This novel processing method could be an alternative to ensure commercial sterilization in the food industry.

Effects of tyndallization temperature on the sterility and quality of kamaboko

In this study, kamaboko gels were tyndallized at various temperatures and sterilization efficiency and impact on quality parameters were assessed. The microbiological, physical, and chemical properties of kamaboko gels were determined throughout the tyndallization process. Superior sterilization efficiency was achieved by tyndallization at a higher temperature; and the combination of heat-induced germination and thermal inactivation of spores was proposed as the main reason. The process had minimal effect on the color of gels. While tyndallized gels heated at 80 °C possessed superior physical properties, all gels showed impaired quality with the progress of heating cycles. Sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) revealed that the cause of alterations in quality differed depending on the processing temperature. This study suggests that the sterility of products could be improved by increasing the processing temperature, time or number of heating cycle.

Outbreaks, Germination, and Inactivation of Bacillus cereus in Food Products: A Review

ABSTRACT

Bacillus cereus has been reported as a foodborne pathogen worldwide. Although food processing technologies to inactivate the pathogen have been developed for decades, foodborne outbreaks related to B. cereus have occurred. In the present review, foodborne outbreaks, germination, inactivation, and detection of B. cereus are discussed, along with inactivation mechanisms. B. cereus outbreaks from 2003 to 2016 are reported based on food commodity, number of cases, and consequent illnesses. Germination before sporicidal treatments is highlighted as an effective way to inactivate B. cereus, because the resistance of the pathogen increases significantly following sporulation. Several germinants used for B. cereus are listed, and their efficacies are compared. Finally, recently used interventions with sporicidal mechanisms are identified, and rapid detection methods that have been developed are discussed. Combining two or more interventions, known as the hurdle technology concept, is suggested to maximize the sporicidal effect. Further study is needed to ensure food safety and to understand germination mechanisms and sporicidal resistance of B. cereus.

HIGHLIGHTS

Environmental determinants influencing anthrax distribution in Queen Elizabeth Protected Area, Western Uganda

Bacillus anthracis, the bacteria that causes anthrax, a disease that primarily affects herbivorous animals, is a soil borne endospore-forming microbe. Environmental distribution of viable spores determines risky landscapes for herbivore exposure and subsequent anthrax outbreaks. Spore survival and longevity depends on suitable conditions in its environment. Anthrax is endemic in Queen Elizabeth Protected Area in western Uganda. Periodic historical outbreaks with significant wildlife losses date to 1950s, but B. anthracis ecological niche in the ecosystem is poorly understood. This study used the Maximum Entropy modeling algorithm method to predict suitable niche and environmental conditions that may support anthrax distribution and spore survival. Model inputs comprised 471 presence-only anthrax occurrence data from park management records of 1956–2010, and 11 predictor variables derived from the World Climatic and Africa Soil Grids online resources, selected considering the ecology of anthrax. The findings revealed predicted suitable niche favoring survival and distribution of anthrax spores as a narrow-restricted corridor within the study area, defined by hot-dry climatic conditions with alkaline soils rich in potassium and calcium. A mean test AUC of 0.94 and predicted probability of 0.93 for anthrax presence were registered. The five most important predictor variables that accounted for 93.8% of model variability were annual precipitation (70.1%), exchangeable potassium (12.6%), annual mean temperature (4.3%), soil pH (3.7%) and calcium (3.1%). The predicted suitable soil properties likely originate from existing sedimentary calcareous gypsum rocks. This has implications for long-term presence of B. anthracis spores and might explain the long history of anthrax experienced in the area. However, occurrence of suitable niche as a restricted hot zone offers opportunities for targeted anthrax surveillance, response and establishment of monitoring strategies in QEPA.

Properties of Aged Spores of Bacillus subtilis

Bacillus spores incubated on plates for 2 to 98 days at 37°C had identical Ca-dipicolinic acid contents, exhibited identical viability on rich- or poor-medium plates, germinated identically in liquid with all germinants tested, identically returned to vegetative growth in rich or minimal medium, and exhibited essentially identical resistance to dry heat and similar resistance to UV radiation. However, the oldest spores had a lower core water content and significantly higher wet heat and NaOCl resistance. In addition, 47- and 98-day spores had lost >98% of intact 16S and 23S rRNA and 97 to 99% of almost all mRNAs, although minimal amounts of mononucleotides were generated in 91 days. Levels of 3-phosphoglyceric acid (3PGA) also fell 30 to 60% in the oldest spores, but how the 3PGA was lost is not clear. These results indicate that (i) translation of dormant spore mRNA is not essential for completion of spore germination, nor is protein synthesis from any mRNA; (ii) in sporulation for up to 91 days at 37°C, the RNA broken down generates minimal levels of mononucleotides; and (iii) the lengths of time that spores are incubated in sporulation medium should be considered when determining conditions for spore inactivation by wet heat, in particular, in using spores to test for the efficacy of sterilization regimens.IMPORTANCE We show that spores incubated at 37°C on sporulation plates for up to 98 days have lost almost all mRNAs and rRNAs, yet the aged spores germinated and outgrew as well as 2-day spores, and all these spores had identical viability. Thus, it is unlikely that spore mRNA, rRNA, or protein synthesis is important in spore germination. Spores incubated for 47 to 98 days also had much higher wet heat resistance than 2-day spores, suggesting that spore "age" should be considered in generating spores for tests of sterilization assurance. These data are the first to show complete survival of hydrated spores for ∼100 days, complementing published data showing dry-spore survival for years.

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

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.

Differential gene expression for investigation of the effect of germinants and heat activation to induce germination in Bacillus cereus spores

Differential gene expression was used to explore the mechanisms underpinning the differences in the impact of heat activation (70 °C for 30 min) on the germination of Bacillus cereus spores in the presence and absence of a germinant (L-alanine). The number of germinated cells, after heat activation plus L-alanine (3.5 ± 0.02 log CFU/ml) in the spore only initial population was found to be higher than that in only heat activated spores (2.01 ± 0.02 log CFU/ml). The concentration of DPA released by heat activated spores in the presence of L-alanine was 68.3 ± 0.1 and 112.1 ± 0.02 μg/ml after 30 and 60 min, compared to 96.5 and 166.2 ± 0.01 μg/ml after 30 and 90 min, respectively released by spores subjected only to heat activation. Gene (BC0784) encoding for the spore germination protein, gerA operon was up-regulated with a log₂-transformed fold change value of 1.2 due to heat activation in the presence of L-alanine. The GerA operon located in the inner membrane is known to be involved in the uptake of L-alanine by B. cereus and has been reported to be involved in L-alanine mediated germination. In addition the up-regulation of genes involved in the uptake of L-alanine is proposed to provide the answer to the synergistic effect of heat and L-alanine in inducing germination in B. cereus spores. In short, heat activation increases the ability of L-alanine to penetrate into the spore's inner membrane, where it can be recognized by the receptors for initiation of the germination pathway. In the current study, the majority of the ribosomal proteins were down-regulated (when spores were heat treated in presence of germinants) this process also appeared to slow down protein synthesis by restricting the protein translation machinery. Differential gene expression revealed the genes responsible for the pathways related to transport and recognition of L-alanine into the spore that could have led to the accelerated germination process along with partial shutting down of protein synthesis pathway and ABC transporters. Knowledge of gene regulation in spores during heat activation will help in the development of approaches to prevent spore germination, which could provide an additional safeguard against bacterial growth and toxin production in improperly cooled heat treated foods.

Spore Germination

Despite being resistant to a variety of environmental insults, the bacterial endospore can sense the presence of small molecules and respond by germinating, losing the specialized structures of the dormant spore, and resuming active metabolism, before outgrowing into vegetative cells. Our current level of understanding of the spore germination process in bacilli and clostridia is reviewed, with particular emphasis on the germinant receptors characterized in Bacillus subtilis, Bacillus cereus, and Bacillus anthracis. The recent evidence for a local clustering of receptors in a "germinosome" would begin to explain how signals from different receptors could be integrated. The SpoVA proteins, involved in the uptake of Ca2+-dipicolinic acid into the forespore during sporulation, are also responsible for its release during germination. Lytic enzymes SleB and CwlJ, found in bacilli and some clostridia, hydrolyze the spore cortex: other clostridia use SleC for this purpose. With genome sequencing has come the appreciation that there is considerable diversity in the setting for the germination machinery between bacilli and clostridia.

Impact of orientation and flexibility of peptide linkers on T. maritima lipase Tm1350 displayed on Bacillus subtilis spores surface using CotB as fusion partner

Fusion protein construction often requires peptide linkers for prolonged conformation, extended stability and enzyme activity. In this study a series of fusion between Thermotoga maritima lipase Tm1350 and Bacillus subtillis coat protein CotB, comprising of several peptide linkers, with different length, flexibility and orientations were constructed. Effects of temperature, pH and chemicals were examined, on the activity of displayed enzyme. The fusion protein with longer flexible linkers L9 [(GGGGS)₄] and L7 (GGGGS-GGGGS-EAAAK-EAAAK-GGGGS-GGGGS) possess 1.29 and 1.16-fold higher activity than the original, under optimum temperature and pH respectively. Moreover, spore surface displaying Tm1350 with L3 (EAAAK-GGGGS) and L9 ((GGGGS)₄) showed extended thermostably, maintaining 1.40 and 1.35-fold higher activity than the original respectively, at 80 °C after 5 h of incubation. The enzyme activity of linkers with different orientation, including L5, L6 and L7 was determined, where L7 maintained 1.05 and 1.27-fold higher activity than L5 and L6. Effect of 0.1% proteinase K, bromelain, 20% ethanol and 30% methanol was investigated. Linkers with appropriate Glycine residues (flexible) showed higher activity than Alanine residues (rigid). The activity of the displayed enzyme can be improved by maintaining orientation and flexibility of peptide linkers, to evaluate high activity and stability in industrial processes.

Clostridium perfringens Sporulation and Sporulation-Associated Toxin Production

The ability of Clostridium perfringens to form spores plays a key role during the transmission of this Gram-positive bacterium to cause disease. Of particular note, the spores produced by food poisoning strains are often exceptionally resistant to food environment stresses such as heat, cold, and preservatives, which likely facilitates their survival in temperature-abused foods. The exceptional resistance properties of spores made by most type A food poisoning strains and some type C foodborne disease strains involve their production of a variant small acid-soluble protein-4 that binds more tightly to spore DNA than to the small acid-soluble protein-4 made by most other C. perfringens strains. Sporulation and germination by C. perfringens and Bacillus spp. share both similarities and differences. Finally, sporulation is essential for production of C. perfringens enterotoxin, which is responsible for the symptoms of C. perfringens type A food poisoning, the second most common bacterial foodborne disease in the United States. During this foodborne disease, C. perfringens is ingested with food and then, by using sporulation-specific alternate sigma factors, this bacterium sporulates and produces the enterotoxin in the intestines.

Survival of Clostridium difficile spores at low water activity

Clostridium difficile is frequently found in meat and meat products. Germination efficiency, defined as colony formation, was previously investigated at temperatures found in meat handling and processing for spores of strain M120 (animal isolate), R20291 (human isolate), and DK1 (beef isolate). In this study, germination efficiency of these spore strains was assessed in phosphate buffered saline (PBS, a_w ∼1.00), commercial beef jerky (a_w ∼0.82/0.72), and a_w-adjusted PBS (a_w ∼0.82/0.72). Surface hydrophobicity was followed for spores stored in PBS. After three months and for all PBS a_w levels tested, M120 and DK1 spores showed a ∼1 decimal reduction in colony formation but this was not the case when kept in beef jerky suggesting a protective food matrix effect. During storage, and with no significant a_w effect, an increase in colony formation was observed for R20291 spores kept in PBS (∼2 decimal log increase) and beef jerky (∼1 decimal log increase) suggesting a loss of spore superdormancy. For all strains, no significant changes in spore surface hydrophobicity were observed after storage. Collectively, these results indicate that depending on the germination properties of C. difficile spores and the media properties, their germination efficiency may increase or decrease during long term food storage.

Spore Heat Activation Requirements and Germination Responses Correlate with Sequences of Germinant Receptors and with the Presence of a Specific spoVA2mob Operon in Foodborne Strains of Bacillus subtilis

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 Bacillus subtilis isolates, encountered in foods, have been attributed to the occurrence of the spoVA^2mob operon carried on the Tn1546 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 spoVA^2mob required higher HA temperatures for efficient germination than spores lacking spoVA^2mob 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.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. subtilis, 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.

Analysis of Germination Capacity and Germinant Receptor (Sub)clusters of Genome-Sequenced Bacillus cereus Environmental Isolates and Model Strains

Spore germination of 17 Bacillus cereus food isolates and reference strains was evaluated using flow cytometry analysis in combination with fluorescent staining at a single-spore level. This approach allowed for rapid collection of germination data under more than 20 conditions, including heat activation of spores, germination in complex media (brain heart infusion [BHI] and tryptone soy broth [TSB]), and exposure to saturating concentrations of single amino acids and the combination of alanine and inosine. Whole-genome sequence comparison revealed a total of 11 clusters of operons encoding germinant receptors (GRs): GerK, GerI, and GerL were present in all strains, whereas GerR, GerS, GerG, GerQ, GerX, GerF, GerW, and GerZ (sub)clusters showed a more diverse presence/absence in different strains. The spores of tested strains displayed high diversity with regard to their sensitivity and responsiveness to selected germinants and heat activation. The two laboratory strains, B. cereus ATCC 14579 and ATCC 10987, and 11 food isolates showed a good germination response under a range of conditions, whereas four other strains (B. cereus B4085, B4086, B4116, and B4153) belonging to phylogenetic group IIIA showed a very weak germination response even in BHI and TSB media. Germination responses could not be linked to specific (combinations of) GRs, but it was noted that the four group IIIA strains contained pseudogenes or variants of subunit C in their gerL cluster. Additionally, two of those strains (B4086 and B4153) carried pseudogenes in the gerK and gerRI (sub)clusters that possibly affected the functionality of these GRs.

IMPORTANCE

Germination of bacterial spores is a critical step before vegetative growth can resume. Food products may contain nutrient germinants that trigger germination and outgrowth of Bacillus species spores, possibly leading to food spoilage or foodborne illness. Prediction of spore germination behavior is, however, very challenging, especially for spores of natural isolates that tend to show more diverse germination responses than laboratory strains. The approach used has provided information on the genetic diversity in GRs and corresponding subclusters encoded by B. cereus strains, as well as their germination behavior and possible associations with GRs, and it provides a basis for further extension of knowledge on the role of GRs in B. cereus (group member) ecology and transmission to the host.

Influences of Various Peptide Linkers on the Thermotoga maritima MSB8 Nitrilase Displayed on the Spore Surface of Bacillus subtilis

In the present study, fusion genes composed of Thermotoga maritima MSB8 nitrilase and Bacillus subtilis 168 outer coat protein CotG were constructed with various peptide linkers and displayed on B. subtilis DB 403 spores. The successful display of CotG-nit fusion proteins on the spore surface of B. subtilis was verified by Western blot analysis and activity measurement. It was demonstrated that the fusion with linker GGGGSEAAAKGGGGS presented the highest thermal and pH stability, which is 2.67- and 1.9-fold of the fusion without linker. In addition, fusion with flexible linker (GGGGS)3 demonstrated better thermal and pH stability than fusions with linkers GGGGS and (GGGGS)2. Fusion with rigid linker (EAAAK) demonstrated better thermal stability than fusions with linkers (EAAAK)2 and (EAAAK)3. Fusions with linker (EAAAK)2 demonstrated better pH stability than fusions with linkers (EAAAK) and (EAAAK)3. In the presence of 1 mM dithiothreitol, 1% (v/v) sodium dodecyl sulfate, and 20% (v/v) ethanol, the optimal linkers of the fusions were MGSSSN, GGGGSEAAAKGGGGS, and (GGGGS)3, respectively. In summary, our results showed that optimizing the peptide linkers with different type, length, and amino acid composition of the fusion proteins would be an efficient way to maintain the stability of fusion proteins and thus improve the nitrilase display efficiency, which could provide an effective method for rational design peptide linkers of displayed nitrilase on B. subtilis.

Variability in DPA and Calcium Content in the Spores of Clostridium Species

Spores of a number of clostridial species, and their resistance to thermal treatment is a major concern for the food industry. Spore resistance to wet heat is related to the level of spore hydration, which is inversely correlated with the content of calcium and dipicolinic acid (DPA) in the spore core. It is widely believed that the accumulation of DPA and calcium in the spore core is a fundamental component of the sporulation process for all endospore forming species. We have noticed heterogeneity in the heat resistance capacity and overall DPA/calcium content among the spores of several species belonging to Clostridium sensu stricto group: two C. acetobutylicum strains (DSM 792 and 1731), two C. beijerinckii strains (DSM 791 and NCIMB 8052), and a C. collagenovorans strain (DSM 3089). A C. beijerinckii strain (DSM 791) and a C. acetobutylicum strain (DSM 792) display low Ca and DPA levels. In addition, these two species, with the lowest average Ca/DPA content amongst the strains considered, also exhibit minimal heat resistance. There appears to be no correlation between the Ca/DPA content and the phylogenetic distribution of the C. acetobutylicum and C. beijerinckii species based either on the 16S rRNA or the spoVA gene. This finding suggests that a subset of Clostridium sensu stricto species produce spores with low resistance to wet heat. Additionally, analysis of individual spores using STEM-EDS and STXM revealed that DPA and calcium levels can also vary amongst individual spores in a single spore population.

Functional Metagenomics of Spacecraft Assembly Cleanrooms: Presence of Virulence Factors Associated with Human Pathogens

Strict planetary protection practices are implemented during spacecraft assembly to prevent inadvertent transfer of earth microorganisms to other planetary bodies. Therefore, spacecraft are assembled in cleanrooms, which undergo strict cleaning and decontamination procedures to reduce total microbial bioburden. We wanted to evaluate if these practices selectively favor survival and growth of hardy microorganisms, such as pathogens. Three geographically distinct cleanrooms were sampled during the assembly of three NASA spacecraft: The Lockheed Martin Aeronautics' Multiple Testing Facility during DAWN, the Kennedy Space Center's Payload Hazardous Servicing Facility (KSC-PHSF) during Phoenix, and the Jet Propulsion Laboratory's Spacecraft Assembly Facility during Mars Science Laboratory. Sample sets were collected from the KSC-PHSF cleanroom at three time points: before arrival of the Phoenix spacecraft, during the assembly and testing of the Phoenix spacecraft, and after removal of the spacecraft from the KSC-PHSF facility. All samples were subjected to metagenomic shotgun sequencing on an Illumina HiSeq 2500 platform. Strict decontamination procedures had a greater impact on microbial communities than sampling location Samples collected during spacecraft assembly were dominated by Acinetobacter spp. We found pathogens and potential virulence factors, which determine pathogenicity in all the samples tested during this study. Though the relative abundance of pathogens was lowest during the Phoenix assembly, potential virulence factors were higher during assembly compared to before and after assembly, indicating a survival advantage. Decreased phylogenetic and pathogenic diversity indicates that decontamination and preventative measures were effective against the majority of microorganisms and well implemented, however, pathogen abundance still increased over time. Four potential pathogens, Acinetobacter baumannii, Acinetobacter lwoffii, Escherichia coli and Legionella pneumophila, and their corresponding virulence factors were present in all cleanroom samples. This is the first functional metagenomics study describing presence of pathogens and their corresponding virulence factors in cleanroom environments. The results of this study should be considered for microbial monitoring of enclosed environments such as schools, homes, hospitals and more isolated habitation such the International Space Station and future manned missions to Mars.

Subboiling Moist Heat Favors the Selection of Enteric Pathogen Clostridium difficile PCR Ribotype 078 Spores in Food

Emerging enteric pathogens could have not only more antibiotic resistance or virulence traits; they could also have increased resistance to heat. We quantified the effects of minimum recommended cooking and higher temperatures, individually on a collection of C. difficile isolates and on the survival probability of a mixture of emerging C. difficile strains. While minimum recommended cooking time/temperature combinations (63–71°C) allowed concurrently tested strains to survive, higher subboiling temperatures reproducibly favored the selection of newly emerging C. difficile PCR ribotype 078. Survival ratios for “ribotypes 078” :  “other ribotypes” (n = 49 : 45 isolates) from the mid-2000s increased from 1 : 1 and 0.7 : 1 at 85°C (for 5 and 10 minutes, resp.) to 2.3 : 1 and 3 : 1 with heating at 96°C (for 5 and 10 minutes, resp.) indicating an interaction effect between the heating temperature and survival of C. difficile genotypes. In multistrain heating experiments, with PCR ribotypes 027 and 078 from 2004 and reference type strain ATCC 9689 banked in the 1970s, multinomial logistic regression (P < 0.01) revealed PCR ribotype 078 was the most resistant to increasing lethal heat treatments. Thermal processes (during cooking or disinfection) may contribute to the selection of emergent specific virulent strains of C. difficile. Despite growing understanding of the role of cooking on human evolution, little is known about the role of cooking temperatures on the selection and evolution of enteric pathogens, especially spore-forming bacteria.

Bacteriocins: Novel Solutions to Age Old Spore-Related Problems?

Bacteriocins are ribosomally synthesized antimicrobial peptides produced by bacteria, which have the ability to kill or inhibit other bacteria. Many bacteriocins are produced by food grade lactic acid bacteria (LAB). Indeed, the prototypic bacteriocin, nisin, is produced by Lactococcus lactis, and is licensed in over 50 countries. With consumers becoming more concerned about the levels of chemical preservatives present in food, bacteriocins offer an alternative, more natural approach, while ensuring both food safety and product shelf life. Bacteriocins also show additive/synergistic effects when used in combination with other treatments, such as heating, high pressure, organic compounds, and as part of food packaging. These features are particularly attractive from the perspective of controlling sporeforming bacteria. Bacterial spores are common contaminants of food products, and their outgrowth may cause food spoilage or food-borne illness. They are of particular concern to the food industry due to their thermal and chemical resistance in their dormant state. However, when spores germinate they lose the majority of their resistance traits, making them susceptible to a variety of food processing treatments. Bacteriocins represent one potential treatment as they may inhibit spores in the post-germination/outgrowth phase of the spore cycle. Spore eradication and control in food is critical, as they are able to spoil and in certain cases compromise the safety of food by producing dangerous toxins. Thus, understanding the mechanisms by which bacteriocins exert their sporostatic/sporicidal activity against bacterial spores will ultimately facilitate their optimal use in food. This review will focus on the use of bacteriocins alone, or in combination with other innovative processing methods to control spores in food, the current knowledge and gaps therein with regard to bacteriocin-spore interactions and discuss future research approaches to enable spores to be more effectively targeted by bacteriocins in food settings.

Spore Resistance Properties

Spores of various Bacillus and Clostridium species are among the most resistant life forms known. Since the spores of some species are causative agents of much food spoilage, food poisoning, and human disease, and the spores of Bacillus anthracis are a major bioweapon, there is much interest in the mechanisms of spore resistance and how these spores can be killed. This article will discuss the factors involved in spore resistance to agents such as wet and dry heat, desiccation, UV and γ-radiation, enzymes that hydrolyze bacterial cell walls, and a variety of toxic chemicals, including genotoxic agents, oxidizing agents, aldehydes, acid, and alkali. These resistance factors include the outer layers of the spore, such as the thick proteinaceous coat that detoxifies reactive chemicals; the relatively impermeable inner spore membrane that restricts access of toxic chemicals to the spore core containing the spore's DNA and most enzymes; the low water content and high level of dipicolinic acid in the spore core that protect core macromolecules from the effects of heat and desiccation; the saturation of spore DNA with a novel group of proteins that protect the DNA against heat, genotoxic chemicals, and radiation; and the repair of radiation damage to DNA when spores germinate and return to life. Despite their extreme resistance, spores can be killed, including by damage to DNA, crucial spore proteins, the spore's inner membrane, and one or more components of the spore germination apparatus.

Spore Cortex Hydrolysis Precedes Dipicolinic Acid Release during Clostridium difficile Spore Germination

Bacterial spore germination is a process whereby a dormant spore returns to active, vegetative growth, and this process has largely been studied in the model organism Bacillus subtilis. In B. subtilis, the initiation of germinant receptor-mediated spore germination is divided into two genetically separable stages. Stage I is characterized by the release of dipicolinic acid (DPA) from the spore core. Stage II is characterized by cortex degradation, and stage II is activated by the DPA released during stage I. Thus, DPA release precedes cortex hydrolysis during B. subtilis spore germination. Here, we investigated the timing of DPA release and cortex hydrolysis during Clostridium difficile spore germination and found that cortex hydrolysis precedes DPA release. Inactivation of either the bile acid germinant receptor, cspC, or the cortex hydrolase, sleC, prevented both cortex hydrolysis and DPA release. Because both cortex hydrolysis and DPA release during C. difficile spore germination are dependent on the presence of the germinant receptor and the cortex hydrolase, the release of DPA from the core may rely on the osmotic swelling of the core upon cortex hydrolysis. These results have implications for the hypothesized glycine receptor and suggest that the initiation of germinant receptor-mediated C. difficile spore germination proceeds through a novel germination pathway.

IMPORTANCE

Clostridium difficile infects antibiotic-treated hosts and spreads between hosts as a dormant spore. In a host, spores germinate to the vegetative form that produces the toxins necessary for disease. C. difficile spore germination is stimulated by certain bile acids and glycine. We recently identified the bile acid germinant receptor as the germination-specific, protease-like CspC. CspC is likely cortex localized, where it can transmit the bile acid signal to the cortex hydrolase, SleC. Due to the differences in location of CspC compared to the Bacillus subtilis germinant receptors, we hypothesized that there are fundamental differences in the germination processes between the model organism and C. difficile. We found that C. difficile spore germination proceeds through a novel pathway.

Survival of Desulfotomaculum spores from estuarine sediments after serial autoclaving and high-temperature exposure

Bacterial spores are widespread in marine sediments, including those of thermophilic, sulphate-reducing bacteria, which have a high minimum growth temperature making it unlikely that they grow in situ. These Desulfotomaculum spp. are thought to be from hot environments and are distributed by ocean currents. Their cells and spores upper temperature limit for survival is unknown, as is whether they can survive repeated high-temperature exposure that might occur in hydrothermal systems. This was investigated by incubating estuarine sediments significantly above (40-80 °C) maximum in situ temperatures (∼ 23 °C), and with and without prior triple autoclaving. Sulphate reduction occurred at 40-60 °C and at 60 °C was unaffected by autoclaving. Desulfotomaculum sp. C1A60 was isolated and was most closely related to the thermophilic D. kuznetsovii(T) (∼ 96% 16S rRNA gene sequence identity). Cultures of Desulfotomaculum sp. C1A60, D. kuznetsovii(T)and D. geothermicum B2T survived triple autoclaving while other related Desulfotomaculum spp. did not, although they did survive pasteurisation. Desulfotomaculum sp. C1A60 and D. kuznetsovii cultures also survived more extreme autoclaving (C1A60, 130 °C for 15 min; D. kuznetsovii, 135 °C for 15 min, maximum of 154 °C reached) and high-temperature conditions in an oil bath (C1A60, 130° for 30 min, D. kuznetsovii 140 °C for 15 min). Desulfotomaculum sp. C1A60 with either spores or predominantly vegetative cells demonstrated that surviving triple autoclaving was due to spores. Spores also had very high culturability compared with vegetative cells (∼ 30 × higher). Combined extreme temperature survival and high culturability of some thermophilic Desulfotomaculum spp. make them very effective colonisers of hot environments, which is consistent with their presence in subsurface geothermal waters and petroleum reservoirs.

Pressure-Based Strategy for the Inactivation of Spores

Since the first application of high hydrostatic pressure (HHP) for food preservation more than 100 years ago, a wealth of knowledge has been gained on molecular mechanisms underlying the HHP-mediated destruction of microorganisms. However, one observation made back then is still valid, i.e. that HHP alone is not sufficient for the complete inactivation of bacterial endospores. To achieve "commercial sterility" of low-acid foods, i.e. inactivation of spores capable of growing in a specific product under typical storage conditions, a combination of HHP with other hurdles is required (most effectively with heat (HPT)). Although HPT processes are not yet industrially applied, continuous technical progress and increasing consumer demand for minimally processed, additive-free food with long shelf life, makes HPT sterilization a promising alternative to thermal processing.In recent years, considerable progress has been made in understanding the response of spores of the model organism B. subtilis to HPT treatments and detailed insights into some basic mechanisms in Clostridium species shed new light on differences in the HPT-mediated inactivation of Bacillus and Clostridium spores. In this chapter, current knowledge on sporulation and germination processes, which presents the basis for understanding development and loss of the extreme resistance properties of spores, is summarized highlighting commonalities and differences between Bacillus and Clostridium species. In this context, the effect of HPT treatments on spores, inactivation mechanism and kinetics, the role of population heterogeneity, and influence factors on the results of inactivation studies are discussed.

The impact of inducing germination of Bacillus anthracis and Bacillus thuringiensis spores on potential secondary decontamination strategies

AIMS

Decontamination and remediation of a site contaminated by the accidental or intentional release of fully virulent Bacillus anthracis spores are difficult, costly and potentially damaging to the environment. Development of novel decontamination strategies that have minimal environmental impacts remains a high priority. Although ungerminated spores are amongst the most resilient organisms known, once exposed to germinants, the germinating spores, in some cases, become susceptible to antimicrobial environments. We evaluated the concept that once germinated, B. anthracis spores would be less hazardous and significantly easier to remediate than ungerminated dormant spores.

METHODS AND RESULTS

Through in vitro germination and sensitivity assays, we demonstrated that upon germination, B. anthracis Ames spores and Bacillus thuringiensis Al Hakam spores (serving as a surrogate for B. anthracis) become susceptible to environmental stressors. The majority of these germinated B. anthracis and B. thuringiensis spores were nonviable after exposure to a defined minimal germination-inducing solution for prolonged periods of time. Additionally, we examined the impact of potential secondary disinfectant strategies including bleach, hydrogen peroxide, formaldehyde and artificial UV-A, UV-B and UV-C radiation, employed after a 60-min germination-induction step. Each secondary disinfectant employs a unique mechanism of killing; as a result, germination-induction strategies are better suited for some secondary disinfectants than others.

CONCLUSIONS

These results provide evidence that the deployment of an optimal combination strategy of germination-induction/secondary disinfection may be a promising aspect of wide-area decontamination following a B. anthracis contamination event.

SIGNIFICANCE AND IMPACT OF THE STUDY

By inducing spores to germinate, our data confirm that the resulting cells exhibit sensitivities that can be leveraged when paired with certain decontamination measures. This increased susceptibility could be exploited to devise more efficient and safe decontamination measures and may obviate the need for more stringent methods that are currently in place.