Long-term fungicide exposure promotes bacterial adaptation and increases virulence of foodborne pathogen Bacillus cereus in Caenorhabditis elegans

The widespread contamination of agricultural soils with pesticides may facilitate the development of antimicrobial resistance and phenotypic adaptations in human pathogens. However, whether one of the most common and clinically significant foodborne pathogens, Bacillus cereus , exhibits such alterations upon long-term exposure to fungicides remains unclear. This study investigated the long-term effects of eight fungicides–chlorothalonil, propineb, tebuconazole, azoxystrobin, propiconazole, mancozeb, carbendazim, and triadimefon–on B. cereus , focusing on changes in biofilm formation, antibiotic susceptibility, and pathogenicity. Results indicated that chlorothalonil, propineb, and tebuconazole completely inhibited bacterial growth at high concentrations, while 30-day exposure to chlorothalonil 8 μM, tebuconazole 500 μM, and propineb 175 μM promoted bacterial adaptation without causing mutation. Adapted strains exhibited enhanced biofilm formation, reduced susceptibility to gentamicin and tetracycline, and greater lethality toward Caenorhabditis elegans . Further qRT-PCR analyses revealed that tebuconazole exposure upregulated genes associated with biofilm development ( purC , purL , and calY ), multidrug efflux pumps ( smr ) associated with antibiotic susceptibility, and virulence factors ( nheC , hblA , hblC , and hblD ). These molecular changes might be associated with the observed increases in biofilm formation, reduced antibiotic susceptibility, and heightened pathogenicity in B. cereus . Overall, these findings demonstrate that prolonged exposure to fungicides can promote adaptations in foodborne pathogens. This work underscores mechanistic insights into fungicide-pathogen interactions relevant to bacterial stress adaptations.