This review summarizes the literature on efficacy of techniques to sterilize soil. Soil may need to be sterilized if contaminated with pathogens such as Bacillus anthracis. Sterilizing soil in-situ minimizes spread of the bio-contaminant. Soil is difficult to sterilize, with efficacy generally diminishing with depth. Methyl bromide, formaldehyde, and glutaraldehyde are the only soil treatment options that have been demonstrated at full-scale to effectively inactivate Bacillus spores. Soil sterilization modalities with high efficacy at bench-scale include wet and dry heat, metam sodium, chlorine dioxide gas, and activated sodium persulfate. Simple oxidants such as chlorine bleach are ineffective in sterilizing soil.

A biosensor is an analytical device whose main components include transducer and bioreceptor segments. The combination of biological recognition with the ligand is followed by transformation into physical or chemical signals. Many publications describe biological sensors as user-friendly, easy, portable, and less time-consuming than conventional methods. Among major categories of methods for the detection of Bacillus anthracis, such as culture-based microbiological method, polymerase chain reaction (PCR) and enzyme-linked immunosorbent assay (ELISA), microarray-based techniques sensors with bioreceptors have been highlighted which particular emphasis is placed on herein. There are several types of biosensors based on various chemical or physical transducers (e.g., electrochemical, optical, piezoelectric, thermal or magnetic electrodes) and the type of biological materials used (e.g., enzymes, nucleic acids, antibodies, cells, phages or tissues). In recent decades, antibody-based sensors have increasingly gained popularity due to their reliability, sensitivity and rapidness. The fundamental principle of antibody-based sensors is mainly based on the molecular recognition between antigens and antibodies. Therefore, immunosensors that detect B. anthracis surface antigens can provide a rapid tool for detecting anthrax bacilli and spores, especially in situ. This review provides a comprehensive summary of immunosensor-based methods using electrochemical, optical, and mass-based transducers to detect B. anthracis.

Bacterial spores are highly resilient and universally present on earth and can irreversibly enter the food chain to cause food spoilage or foodborne illness once revived to resume vegetative growth. Traditionally, extensive thermal processing has been employed to efficiently kill spores; however, the relatively high thermal load adversely affects food quality attributes. In recent years, the germination-inactivation strategy has been developed to mildly kill spores based on the circumstance that germination can decrease spore-resilient properties. However, the failure to induce all spores to geminate, mainly owing to the heterogeneous germination behavior of spores, hampers the success of applying this strategy in the food industry. Undoubtedly, elucidating the detailed germination pathway and underlying mechanism can fill the gap in our understanding of germination heterogeneity, thereby facilitating the development of full-scale germination regimes to mildly kill spores. In this review, we comprehensively discuss the mechanisms of spore germination of Bacillus and Clostridium species, and update the molecular basis of the early germination events, for example, the activation of germination receptors, ion release, Ca-DPA release, and molecular events, combined with the latest research evidence. Moreover, high hydrostatic pressure (HHP), an advanced non-thermal food processing technology, can also trigger spore germination, providing a basis for the application of a germination-inactivation strategy in HHP processing. Here, we also summarize the diverse germination behaviors and mechanisms of spores of Bacillus and Clostridium species under HHP, with the aim of facilitating HHP as a mild processing technology with possible applications in food sterilization. Practical Application: This work provides fundamental basis for developing efficient killing strategies of bacterial spores in food industry.

Light-emitting diodes (LEDs) is an eco-friendly light source with broad-spectrum antimicrobial activity. Recent studies have extensively been conducted to evaluate its efficacy in microbiological safety and the potential as a preservation method to extend the shelf-life of foods. This review aims to present the latest update of recent studies on the basics (physical, biochemical and mechanical basics) and antimicrobial activity of LEDs, as well as its application in the food industry. The highlight will be focused on the effects of LEDs on different types (bacteria, yeast/molds, viruses) and forms (planktonic cells, biofilms, endospores, fungal toxin) of microorganisms. The antimicrobial activity of LEDs on various food matrices was also evaluated, together with further analysis on the food-related factors that lead to the differences in LEDs efficiency. Besides, the applications of LEDs on the food-related conditions, packaged food, and equipment that could enhance LEDs efficiency were discussed to explore the future trends of LEDs technology in the food industry. Overall, the present review provides important insights for future research and the application of LEDs in the food industry.

Spore-forming bacteria are resistant to stress conditions owing to their ability to form highly resistant dormant spores. These spores can survive adverse environmental conditions in nature, as well as decontamination processes in the food and related industries. Bacterial spores may return to their vegetative state through a process called germination. As spore germination is critical for the loss of resistance, outgrowth, and development of pathogenicity and spoilage potential, the germination pathway has piqued the interest of the scientific community. The inhibition and induction of germination have critical applications in the food industry. Targeted germination can aid in decreasing the resistance of spores and allow the application of milder inactivation procedures. This germination-inactivation strategy allows better maintenance of important food quality attributes. Different stimuli are reported to trigger germination. Among those, isostatic high pressure (HP) has gained increasing attention due to its potential applications in industrial processes. However, pressure-mediated spore germination is extremely heterogeneous as some spores germinate rapidly, while others exhibit slow germination or do not undergo germination at all. The successful and safe implementation of the germination-inactivation strategy, however, depends on the germination of all spores. Therefore, there is a need to elucidate the mechanisms of HP-mediated germination. This work aimed to critically review the current state of knowledge on Bacillus spore germination at a moderate HP of 50-300 MPa. In this review, the germination mechanism, heterogeneity, and influencing factors have been outlined along with knowledge gaps.

Clostridioides difficile, a spore-forming anaerobe, resides in the intestine. The life cycle of C. difficile illustrates an interdependent relationship between bile acids, commensal microbiota, and C. difficile. Primary bile acids are critical for the germination of C. difficile spores in the small intestine, while secondary bile acids serve as a counterbalance to inhibit the growth of the organism in the colon. Many commensal bacteria especially Clostridium spp. are responsible for transforming primary bile acids into secondary bile acids. Antibiotics eliminate bacteria that convert primary bile acids into secondary bile acids and, thus, allow C. difficile to flourish and cause diarrhea. In children younger than 2 years of age, who normally only produce primary bile acids, colonization with toxin-producing C. difficile is exceedingly common. The reason for the absence of C. difficile diarrhea in the children remains unexplained.

The ever-increasing applications of enzymes are limited by the relatively poor performance in harsh processing conditions. As a result, there are constant innovations in immobilization protocols for improving biocatalyst activity and stability. Bacterial spores are cheap to generate and highly resistant to environmental stress. The spore core is sheathed by an inner membrane, the germ cell wall, the cortex, outer membrane, spore coat and in some species the exosporium. The spore surface is anion-rich, hydrophobic and contains several reactive groups capable of interacting and stabilizing enzyme molecules through electrostatic forces, hydrophobic interactions and covalent bonding. The probiotic nature of spores obtained from non-toxic bacterial species makes them suitable carriers for the enzyme immobilization, especially food-grade enzymes or those intended for therapeutic use. Immobilization on spores is by direct adsorption, covalent attachment or surface display during the sporulation phase. Hindrances to the immobilization on spore matrix include the production rates, operational instability, and reduced catalytic properties due to conformational changes in enzyme. This paper reviews bacterial spore as a heterofunctional support matrix gives reasons why probiotic bacillus spores are better options and the diverse technologies adopted for spore-enzyme immobilization. It further suggests directions for future use and discusses the commercialization prospects.

UNASSIGNED: 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.
CONCLUSIONS:

Clostridioides difficile typing is invaluable for the investigation of both institution-specific outbreaks as well as national surveillance. While the epidemic ribotype 027 (RT027) has received a significant amount of resources and attention, ribotype 106 (RT106) has become more prevalent throughout the past decade. The purpose of this systematic review was to comprehensively summarize the genetic determinants, antimicrobial susceptibility, epidemiology, and clinical outcomes of infection caused by RT106. A total of 68 articles published between 1999 and 2019 were identified as relevant to this review. Although initially identified in the United Kingdom in 1999, RT106 is now found worldwide and became the most prevalent strain in the United States in 2016. Current data indicate that RT106 harbors the tcdA and tcdB genes, lacks binary toxin genes, and does not contain any deletions in the tcdC gene, which differentiates it from other epidemic strains, including ribotypes 027 and 078. Interestingly, RT106 produces more spores than other strains, including RT027. Overall, RT106 is highly resistant to erythromycin, clindamycin, fluoroquinolones, and third-generation cephalosporins. However, the MIC90 in most studies are one to two fold dilutions below the epidemiologic cut-off values of metronidazole and vancomycin, suggesting both are acceptable treatment options from an in vitro perspective. The few clinical outcomes studies available concluded that RT106 causes less severe disease than RT027, but patients were significantly more likely to experience multiple CDI relapses when infected with a RT106 strain. Specific areas warranting future study include potential survival advantages provided by genetic elements as well as a more robust investigation of clinical outcomes associated with RT106.

Recent developments in preservation technologies allow for the delivery of food with nutritional value and superior taste. Of special interest are low-acid, shelf-stable foods in which the complete control or inactivation of bacterial endospores is the crucial step to ensure consumer safety. Relevant preservation methods can be classified into physicochemical or physical hurdles, and the latter can be subclassified into thermal and nonthermal processes. The underlying inactivation mechanisms for each of these physicochemical or physical processes impact different morphological or molecular structures essential for spore germination and integrity in the dormant state. This review provides an overview of distinct endospore defense mechanisms that affect emerging physical hurdles as well as which technologies address these mechanisms. The physical spore-inactivation technologies considered include thermal, dynamic, and isostatic high pressure and electromagnetic technologies, such as pulsed electric fields, UV light, cold atmospheric pressure plasma, and high- or low-energy electron beam.