Characterization of the Toxigenic Potential of Bacillus cereus sensu lato Isolated from Raw Berries and Their Products

Genetic Profile and Toxigenic Potential of Bacillus cereus Isolates from a Norwegian Ice Cream Production Plant

Members of the B. cereus group are spore-forming organisms commonly associated with spoilage of milk and dairy products. We have determined the genetic identity and growth characteristics of 57 B. cereus isolates collected from a Norwegian ice cream production plant. Our findings revealed persistence of B. cereus spp. strains for up to 19 months, suggesting the plant's susceptibility to long-term colonization. One of the mesophilic isolates, NVH-YM303, carried a complete cereulide synthetase operon. To assess the potential food poisoning risk associated with the presence of cereulide-producing strains in the production line, we examined the production of cereulide in ice cream and milk at different temperatures by NVH-YM303 and by the emetic psychrotrophic B. weihenstephanensis strain BtB2-4. Our findings revealed that NVH-YM303 produced higher levels of cereulide in ice cream as compared to milk. Furthermore, it was observed that NVH-YM303 produced more cereulide in ice cream at 25 °C compared to 15 °C. Conversely, BtB2-4 produced more cereulide in ice cream at 15 °C than at 25 °C. The results obtained in this study contribute to knowledge important for risk assessment of the potential hazards posed by the presence of B. cereus within ice cream production facilities.

Entomopathogenic Bacillus cereus impairs the fitness of the spotted-wing drosophila, Drosophila suzukii

Drosophila suzukii is a notorious pest which causes devastating damage to thin-skinned fruits, and the larvae feed on the fruit, causing extensive agricultural economic loss. The current application of insecticides to manage this pest results in serious resistance and environmental hazards, so an alternative strategy for D. suzukii biocontrol is urgently needed. Here, we reported that entomopathogenic Bacillus cereus has the potential to biocontrol D. suzukii. We isolated and identified the bacterial strain, B. cereus H1, that was detrimental to the fitness of both D. suzukii progenies and parents. D. suzukii was robustly repelled to depositing eggs on the halves with metabolites of B. cereus H1. Both males and females of D. suzukii were susceptible to B. cereus H1. B. cereus H1 significantly arrested larval development with at least 40% lethal larvae. The median lethal time (LT50) of males and females of D. suzukii challenged with B. cereus H1 was 3 and 2 d, respectively. Moreover, B. cereus H1 disrupted the intestinal integrity and pH value of D. suzukii and resulted in an increase in bacterial load of guts and hemolymph. Mechanistically, infection of B. cereus H1 led to the activation of the dual oxidase (DUOX)-ROS-Jun N-terminal kinase (JNK) pathway. The findings showed that the entomopathogen B. cereus H1 could potentially act as a biological control agent against D. suzukii, advancing fundamental concepts of integrated pest management programs against D. suzukii.

Investigating the Role of OrbF in Biofilm Biosynthesis and Regulation of Biofilm-Associated Genes in Bacillus cereus BC1

Bacillus cereus (B. cereus), a prevalent foodborne pathogen, constitutes a substantial risk to food safety due to its pronounced resilience under adverse environmental conditions such as elevated temperatures and ultraviolet radiation. This resilience can be attributed to its capacity for biofilm synthesis and sustained high viability. Our research aimed to elucidate the mechanisms governing biofilm biosynthesis in B. cereus. To this end, we constructed a 5088-mutant library of the B. cereus strain BC1 utilizing the transposon TnYLB-1. Systematic screening of this library yielded mutants exhibiting diminished biofilm formation capabilities. Twenty-four genes associated with the biofilm synthesis were identified by reverse PCR in these mutants, notably revealing a significant reduction in biofilm synthesis upon disruption of the orbF gene in B. cereus BC1. Comparative analysis between the wild type and orbF-deficient BC1 strains (BC1ΔorbF) indicated a marked downregulation (decreased by 11.7% to 96.7%) in the expression of genes implicated in biofilm formation, flagellar assembly, and bacterial chemotaxis in the BC1ΔorbF. Electrophoretic mobility shift assay (EMSA) further corroborated the role of OrbF, demonstrating its binding to the promoter region of the biofilm gene cluster, subsequently leading to the suppression of transcriptional activity of biofilm-associated genes in B. cereus BC1. Our findings underscore the pivotal role of orbF in biofilm biosynthesis in B. cereus, highlighting its potential as a target for strategies aimed at mitigating biofilm formation in this pathogen.