VIRBT

Bacillus thuringiensis is a bacterium increasingly used as microbial insecticide to fight lepidopteran larvae, a major crop pest. Recently, this bacterium has also been involved in food poisoning and systemic infections, affecting humans, wildlife and the environment indiscriminately. As part of the "One Health" concept, our project tackles the mechanism of virulence of this bacterium using insects, mice and human cell culture and combining medicine, immunology, cell biology, genetics and bioinformatics. It contributes to the topic "Assessment and detection of anthropogenic risks to human health”.

The use of chemical pesticides is controversial, mainly because of their harmful effects on the environment and human health. The emerging solution is the use of biocontrol agents, also called biopesticides. Like chemical pesticides, biopesticides are used to combat certain organisms considered harmful, but by means of natural substances (plant extracts, pheromones, essential oils, etc.) or organisms (predators such as ladybirds, bacteria, viruses, etc.). These natural pesticides are a good alternative to chemical ones, but not without a risk to human health. The microbial insecticide Bacillus thuringiensis (Bt), although an "organic" pesticide, is involved in almost 20% of cases of food poisoning caused by the Bacillus cereus group of bacteria to which it belongs (Bonis et al., PLOS One, 2021). Some strains of the Bacillus cereus group have also been found responsible for nosocomial diseases (such as septicemia) in weakened individuals (e.g., immunocompromised individuals, the elderly, newborns). So far, we have ignored how this group of bacteria displays its virulence and to what extent the hazard coming from Bt in food originates from agriculture. This is what the consortium of researchers working on the VirBt project is trying to investigate and understand. Focusing on Bt and its effects, biologists from ISA, C3M, Nice CHU and the Laboratory for Food Safety of the ANSES Maisons-Alfort are working together to assess the virulence of Bt strains. They are also investigating the extent to which weakened individuals are prone to Bt infection and more broadly to infection by the Bacillus cereus group. To achieve this, three models are being used in the experiments: Drosophila (fruit fly), mice and human intestinal cell cultures. Drosophila is a well-established model for studying the innate immune system because it presents strong similarities with mammals, including mice and humans. Furthermore, the use of Drosophila complies with ethical requirements by first testing the virulence of many Bacillus strains on Drosophila, before selecting a limited number of strains and testing them on mice. The data obtained from these models will then be correlated with those recovered from human patient samples. Initial results from tests on Drosophila show that Bt storage is most concentrated in the intestinal tract, sporadically leading to diarrhea and intestinal disorders as early as 8 to 24 hours after ingestion.
While Bt strains are the most effective of all pesticides, they are also the ones to which people are most exposed. The survey conducted by ANSES as part of the project highlights this exposure. After collecting and testing 161 fruits and vegetables commercially certified "Organic Agriculture", almost 50% of the products tested came up positive for Bt. Peppers, tomatoes, apples, cucumbers, aromatic herbs, etc., were all in the same basket! Importantly, no Bt of agricultural origin has been identified in any of the 45 patients analyzed so far with septicemia caused by bacteria from the Bacillus cereus group. This observation suggests that Bt used as a microbial pesticide, though present in fruits and vegetables, may be partly responsible for food poisoning but is unlikely to be involved in septicemia in weakened patients.
Research conducted jointly by biologists and public health professionals should lead to the development of tools to assess and detect these Bt strains more easily in food and in the body, and should make it safer to use them in agriculture, since today neither dose limits nor a delay before harvest are imposed.

• Tleiss F., Montanari M., Pierre O., Royet J., Osman D., Gallet A. and Kurz C.L.: "Spatial and temporal coordination of Duox/TrpA1/Dh31 and IMD pathways is required for the efficient elimination of pathogenic bacteria in the intestine of Drosophila larvae". eLife, June 17, 13:RP98716 (2024) https://doi.org/10.7554/eLife.98716.1
• Fichant A., Lanceleur R., Hachfi S., Brun-Barale A., Blier A.L., Firmesse O., Gallet A., Fessard V. and Bonis M.: "New approach methods to assess the enteropathogenic potential of strains of the Bacillus cereus group including Bacillus thuringiensis". Foods 13(8), 1140 (2024). https://doi.org/10.3390/foods13081140
• Fichant A., Felten A., Gallet A., Firmesse O., Bonis M.: "Identification of genetic markers for the discrimination of Bacillus thuringiensis within the Bacillus cereus group, in the context of foodborne outbreaks". Foods 11(23), 3924 (2022) https://doi.org/10.3390/foods11233924
• Armel GALLET Seminar at the invitation of Léopold Kurz: "Bacillus, Environnement et Santé", UMR 7288, Institut de Biologie du Développement de Marseille (France, October 6, 2023)
• Armel GALLET Chairperson: Symbionts session, Jacques Monod conference, Insect Models For Infection Biology, (Roscoff, France, June 26 to 30, 2023)
• Armel GALLET Poster: "Ingestion of Bacillus cereus spores dampens the immune response to favor bacterial persistence". Jacques Monod conference, Insect Models For Infection Biology, (Roscoff, France, June 26 to 30, 2023)
• Armel GALLET Seminar at the invitation of V. Broussolle: "Ingestion of Bacillus cereus spores dampens the intestinal immune response to favor bacterial persistence". UMR408 Sécurité et Qualité des Produits d'Origine Végétale, Centre INRAE PACA (Avignon, France, May 31, 2023).
• Arnaud FICHANT communication: "Characterization of the virulence potential of spore-forming Bacillus cereus in Drosophila melanogaster", 10th European Spores Conference (Cambridge, United Kingdom, April 2023)
• Mathilde BONIS, communication: "New approach methodologies to assess the virulence potency of enteropathogenic Bacillus cereus" (BSPIT congress: Bactéries sporulantes pathogènes ou d'intérêt technologique; November 2023)
• Fichant, A.; Lanceleur, R.; Hachfi, S.; Brun-Barale, A.; Blier, A.-L.; Firmesse, O.; Gallet, A.; Fessard, V.; Bonis, M. New Approach Methods to Assess the Enteropathogenic Potential of Strains of the Bacillus cereus Group, including Bacillus thuringiensis. Foods 2024, 13, 1140. https://doi.org/10.3390/foods13081140