Ecological Role of Widespread Bacteriocin Production among Bacillus cereus Contaminating Dairy Products and Characterization of Three Cereins

Bacillus cereus is a ubiquitous spore-forming gram-positive bacterium. The antibacterial molecules or bacteriocins provide an ecological advantage to B. cereus and promote its proliferation in the bacterial communities and food contamination. The goal of the present work was to detect and identify the antimicrobial activity potential of 114 B. cereus food strains. It aimed at accessing the ecological status of B. cereus variants and characterizing the bacteriocins. An inhibitory activity was detected in 61.4% of the collection. Three selected isolates were found to be bacteriocin (cerein) producers and were identified as B. cereus by 16S rRNA gene sequencing. The cerein activities were inhibited by at least one protease treatment. They were stable within a wide range of pH, sustained heat treatments (up to 96 degrees C for 30 min) and treatment with organic solvents and detergents. These cereins showed bactericidal and bacteriolytic effects. They belonged to class II of bacteriocins. The three cereins were produced at the early stationary phase and remained stable until 50 h of cultivation. The preparation trough SDS PAGE gave an inhibitory zone with an apparent molecular weight of about 10 kDa to the three cereins. The three selected bacteriocins produced by B. cereus dairy strains deserve further research of their potential in pathogen control. Bacteriocin production may play a key role in the ubiquitous distribution of B. cereus and his persistency in dairy products.