UV-C and wet heat resistance of Bacillus thuringiensis biopesticide endospores compared to foodborne Bacillus cereus endospores

Inactivation mechanisms of carvacrol on Salmonella Typhimurium and its combined inhibitory effects with blue light-405 nm for chicken meat preservation

Salmonella Typhimurium (S. Typhimurium) is a major contributor responsible for food contamination and foodborne illnesses. In this study, the antibacterial activity of natural compound carvacrol (CAR) against S. Typhimurium were evaluated, and the combined inhibitory effects of CAR and blue light-405 nm (BL-405 nm) were also assessed for chicken meat preservation. CAR showed efficient antibacterial activity with a minimal inhibitory concentration (MIC) at 0.5 mg/mL. CAR at 2MIC significantly compromised bacterial membrane integrity, resulting in intracellular content leakage. The combined effect of CAR and BL-405 nm achieved a remarkable 5.62 log CFU/mL reduction in S. Typhimurium viability. The antibacterial mechanism investigations demonstrated that BL-405 nm and CAR triggered the cell oxidative stress by producing highly reactive oxygen species, such as reactive hydroxyl radicals (OH), leading to cellular destruction and ultimately resulting in cell death. In practical application test, CAR combined with BL-405 nm treatment effectively extended chicken meat shelf life by maintaining moisture content, stabilizing pH, preserving color and texture, and inhibiting microbial growth and lipid oxidation. The study provided novel insights into the antibacterial mechanisms of CAR combined with BL-405 nm against S. Typhimurium, which could offer a new strategy for extending the shelf life of poultry meat.

Whole-genome sequencing and secondary metabolite exploration of the novel Bacillus velezensis BN with broad-spectrum antagonistic activity against fungal plant pathogens

The utilization of chemical pesticides recovers 30%-40% of food losses. However, their application has also triggered a series of problems, including food safety, environmental pollution, pesticide resistance, and incidents of poisoning. Consequently, green pesticides are increasingly seen as viable alternatives to their chemical counterparts. Among these, Plant Growth-Promoting Rhizobacteria (PGPR), which are found within plant rhizosphere, stand out for their capacity to stimulate plant growth. Recently, we isolated a strain, BN, with broad-spectrum antimicrobial activity from the rhizosphere of Lilium brownii. Identification revealed that this strain belongs to the species Bacillus velezensis and exhibits significant inhibitory effects against various fungal plant pathogens. The complete genome sequence of B. velezensis BN consists of a circular chromosome with a length of 3,929,791 bp, includes 3,747 protein-coding genes, 81 small RNAs, 27 rRNAs, and 86 tRNAs. Genomic analysis revealed that 29% of the genes are directly involved in plant growth, while 70% of the genes are indirectly involved. In addition, 12 putative biosynthetic gene clusters were identified, responsible for the synthesis of secondary metabolites, such as non-ribosomal peptides, lanthipeptides, polyketides, siderophores, and terpenes. These findings provide a scientific basis for the development of efficient antimicrobial agents and the construction of biopesticide production platforms in chassis cells.

Sublethal Damage Caused by Cold Plasma on Bacillus cereus Cells: Impact on Cell Viability and Biofilm-Forming Capacity

The Bacillus cereus group represents a serious risk in powdered and amylaceous foodstuffs. Cold plasma (the fourth state of matter) is emerging as an alternative effective nonthermal technology for pasteurizing a wide range of matrices in solid, liquid, and powder form. The present study aims to evaluate the mechanisms involved in Bacillus cereus inactivation via cold plasma, focusing on (i) the technology's ability to generate damage in cells (at the morphological and molecular levels) and (ii) studying the effectiveness of cold plasma in biofilm mitigation through the direct effect and inhibition of the biofilm-forming capacity of sublethally damaged cells post-treatment. Dielectric barrier discharge cold plasma (DBD-CP) technology was used to inactivate B. cereus, B. thuringiensis, and B. mycoides under plasma power settings of 100, 200, and 300 W and treatment times ranging from 1 to 10 min. Inactivation levels were achieved in 2-7 log10 cycles under the studied conditions. Percentages of sublethally damaged cells were observed in a range of 45-98%, specifically at treatment times below 7 min. The sublethally damaged cells showed poration, erosion, and loss of integrity at the superficial level. At the molecular level, proteins and DNA leakage were also observed for B. cereus but were minimal for B. mycoides. Biofilms formed by B. cereus were progressively disintegrated under the DBD-CP treatment. The greater the CP treatment intensity, the greater the tearing of the bacteria's biofilm network. Additionally, cells sublethally damaged by DBD-CP were evaluated in terms of their biofilm-forming capacity. Significant losses in the damaged cells' biofilm network density and aggregation capacity were observed when B. cereus was recovered after inactivation at 300 W for 7.5 min, compared with the untreated cells. These results provide new insights into the future of tailored DBD-CP design conditions for both the inactivation and biofilm reduction capacity of B. cereus sensu lato species, demonstrating the effectiveness of cold plasma and the risks associated with sublethal damage generation.

Comparing resistance of bacterial spores and fungal conidia to pulsed light and UVC radiation at a wavelength of 254 nm

Pulsed light (PL) inactivates microorganisms by UV-rich, high-irradiance and short time pulses (250 μs) of white light with wavelengths from 200 nm to 1100 nm. PL is applied for disinfection of food packaging material and food-contact equipment. Spores of seven Bacillus ssp. strains and one Geobacillus stearothermophilus strain and conidia of filamentous fungi (One strain of Aspergillus brasiliensis, A. carbonarius and Penicillium rubens) were submitted to PL (fluence from 0.23 J/cm2 to 4.0 J/cm2) and UVC (at λ = 254 nm; fluence from 0.01 J/cm2 to 3.0 J/cm2). One PL flash at 3 J/cm2 allowed at least 3 log-reduction of all tested microorganisms. The emetic B. cereus strain F4810/72 was the most resistant of the tested spore-forming bacteria. The PL fluence to 3 log-reduction (F3 PL) of its spores suspended in water was 2.9 J/cm2 and F3 UVC was 0.21 J/cm2, higher than F3 PL and F3 UVC of spores of B. pumilus SAFR-032 2.0 J/cm2 and 0.15 J/cm2, respectively), yet reported as a highly UV-resistant spore-forming bacterium. PL and UVC sensitivity of bacterial spores was correlated. Aspergillus spp. conidia suspended in water were poorly sensitive to PL. In contrast, PL inactivated Aspergillus spp. conidia spread on a dry surface more efficiently than UVC. The F2 PL of A. brasiliensis DSM1988 was 0.39 J/cm2 and F2 UVC was 0.83 J/cm2. The resistance of spore-forming bacteria to PL could be reasonably predicted from the knowledge of their UVC resistance. In contrast, the sensitivity of fungal conidia to PL must be specifically explored.

Effect of novel and conventional food processing technologies on Bacillus cereus spores

This chapter provides a summary of the effect of thermal and non-thermal processing technologies on Bacillus cereus spores, a well-known pathogenic bacterium associated with foodborne illnesses. B. cereus has been frequently detected in rice, milk products, infant food, liquid eggs products and meat products all over the world. This Gram positive, rod-shaped, facultative anaerobe can produce endospores that can withstand pasteurization, UV radiation, and chemical reagents commonly used for sanitization. B. cereus spores can germinate into vegetative cells that can produce toxins. The conventional regime for eliminating spores from food is retorting which uses the application of high temperature (121 °C). However, at this temperature, there could be a significant amount of loss in the organoleptic and functional qualities of the food components, especially proteins. This leads to the research on the preventive measures against germination and if possible, to reduce the resistance before using a non-thermal technology (temperatures less than retorting-121 °C) for inactivation. This chapter reviews the development and success of several food processing technologies in their ability to inactivate B. cereus spores in food.