Foodborne spore-forming bacteria: Challenges and opportunities for their control through the food production chain

Foodborne spore-forming bacteria represent a significant challenge within the food production chain due to their widespread occurrence and resistance to various processing methods. In addition to their role in food spoilage, these bacteria exhibit pathogenic properties, posing risks to public health. A comprehensive understanding of the impact of unit operations along the food production continuum, from farm or field to fork, is essential for ensuring both the safety and quality of food products. This chapter explores the factors influencing the growth, inactivation, and persistence of these bacteria, as well as the challenges and opportunities for their control. The discussion encompasses preventive measures, control strategies at the farm and field levels, and processing operations, including both thermal and non-thermal methods. Post-processing controls, such as storage and distribution practices, are also addressed. Furthermore, consumer behavior, education, and lessons learned from past outbreaks and product recalls contribute to a broader understanding of how to manage spore-forming bacteria within the food production chain. By assessing and quantifying the effects of each processing step, it becomes possible to implement effective control measures, thereby ensuring microbiological safety and enhancing the quality of food products.

New Thoughts on an Old Topic: Secrets of Bacterial Spore Resistance Slowly Being Revealed

The quest for bacterial survival is exemplified by spores formed by some Firmicutes members. They turn up everywhere one looks, and their ubiquity reflects adaptations to the stresses bacteria face. Spores are impactful in public health, food safety, and biowarfare. Heat resistance is the hallmark of spores and is countered principally by a mineralized gel-like protoplast, termed the spore core, with reduced water which minimizes macromolecular movement/denaturation/aggregation. Dry heat, however, introduces mutations into spore DNA. Spores have countermeasures to extreme conditions that are multifactorial, but the fact that spore DNA is in a crystalline-like nucleoid in the spore core, likely due to DNA saturation with small acid-soluble spore proteins (SASPs), suggests that reduced macromolecular motion is also critical in spore dry heat resistance. SASPs are also central in the radiation resistance characteristic of spores, where the contributions of four spore features-SASP; Ca2+, with pyridine-2,6-dicarboxylic acid (CaDPA); photoproduct lyase; and low water content-minimize DNA damage. Notably, the spore environment steers UV photochemistry toward a product that germinated spores can repair without significant mutagenesis. This resistance extends to chemicals and macromolecules that could damage spores. Macromolecules are excluded by the spore coat which impedes the passage of moieties of ≥10 kDa. Additionally, damaging chemicals may be degraded or neutralized by coat enzymes/proteins. However, the principal protective mechanism here is the inner membrane, a compressed structure lacking lipid fluidity and presenting a barrier to the diffusion of chemicals into the spore core; SASP saturation of DNA also protects against genotoxic chemicals. Spores are also resistant to other stresses, including high pressure and abrasion. Regardless, overarching mechanisms associated with resistance seem to revolve around reduced molecular motion, a fine balance between rigidity and flexibility, and perhaps efficient repair.

What's new and notable in bacterial spore killing!

Spores of many species of the orders Bacillales and Clostridiales can be vectors for food spoilage, human diseases and intoxications, and biological warfare. Many agents are used for spore killing, including moist heat in an autoclave, dry heat at elevated temperatures, UV radiation at 254 and more recently 222 and 400 nm, ionizing radiation of various types, high hydrostatic pressures and a host of chemical decontaminants. An alternative strategy is to trigger spore germination, as germinated spores are much easier to kill than the highly resistant dormant spores—the so called “germinate to eradicate” strategy. Factors important to consider in choosing methods for spore killing include the: (1) cost; (2) killing efficacy and kinetics; (3) ability to decontaminate large areas in buildings or outside; and (4) compatibility of killing regimens with the: (i) presence of people; (ii) food quality; (iii) presence of significant amounts of organic matter; and (iv) minimal damage to equipment in the decontamination zone. This review will summarize research on spore killing and point out some common flaws which can make results from spore killing research questionable.

Dodecylamine rapidly kills of spores of multiple Firmicute species: properties of the killed spores and the mechanism of the killing

AIMS

Previous work showed that Bacillus subtilis dormant spore killing and germination by dodecylamine take place by different mechanisms. This new work aimed to optimize killing of B. subtilis and other Firmicutes spores and to determine the mechanism of the killing.

METHODS AND RESULTS

Spores of seven Firmicute species were killed rapidly by dodecylamine under optimal conditions and more slowly by decylamine or tetradecylamine. The killed spores were not recovered by additions to recovery media, and some of the killed spores subsequently germinated, all indicating that dodecylamine-killed spores truly are dead. Spores of two species treated with dodecylamine were more sensitive to killing by a subsequent heat treatment, and spore killing of at least one species was faster with chemically decoated spores. The cores of dodecylamine-killed spores were stained by the nucleic acid stain propidium iodide, and dodecylamine-killed wild-type and germination-deficient spores released their stores of phosphate-containing small molecules.

CONCLUSIONS

This work indicates that dodecylamine is likely a universal sporicide for Firmicute species, and it kills spores by damaging their inner membrane, with attendant loss of this membrane as a permeability barrier.

SIGNIFICANCE AND IMPACT OF THE STUDY

There is a significant need for agents that can effectively kill spores of a number of Firmicute species, especially in wide area decontamination. Dodecylamine appears to be a universal sporicide with a novel mechanism of action, and this or some comparable molecule could be useful in wide area spore decontamination.

Measuring Heat Production from Burning Al/Zr and Al/Mg/Zr Composite Particles in a Custom Micro-Bomb Calorimeter

Al:Zr, Al-8Mg:Zr, and Al-38Mg:Zr nanocomposite particles fabricated by physical vapor deposition (PVD) and ball milling were reacted in 1 atm of pure O2 within a custom, highly-sensitive micro-bomb calorimeter. The heats of combustion were compared to examine the effect of particle size and composition on combustion efficiency under room temperature and in a fixed volume. All particles yielded ~60-70% of their theoretical maximum heat of combustion and exhibited an increase in heat over composite thin films of similar compositions, which is attributed to an increase in the surface area to volume ratio. The effect of particle size and geometry are mitigated owing to the sintering of the particles within the crucible, implying the importance of particle dispersion for enhanced performance. Vaporization of the metal species may transition between two diffusion flame species (Mg to Al). As Mg content is increased, more vaporization may occur at lower temperatures, leading to an additional stage of sintering. Physically intermixed Al and Mg oxides have been observed coating the surface of the particles, which implies a continuous transition of these vaporization processes. Such nano-oxides imply high vapor-flame combustion temperatures (>2700 K) and suggest viability for agent defeat applications.