Isolation and characterization of phages infecting Bacillus cereus

Aim: To isolate and characterize bacteriophages (phages) that infect the foodborne pathogen Bacillus cereus. Methods and Results: Two phages were isolated from soil based on their ability to form plaques on four indicator hosts including Bacillus thuringiensis subsp. israelensis, and three isolates of B. cereus. The purified phages were characterized by morphology, host range, single-step growth curves and restriction enzyme digestion profiles. The phages appeared to be of the Myoviridae family based on their structure in electron micrographs. The phages lysed bacteria of several species, produced average burst sizes of 322 and 300 phages per infected cell, and both had genomes over 90 kb. The phages were chloroform-resistant and stable at 4 degrees C. They reduced the concentration of B. cereus in mashed potatoes by > 6 log(10) CFU ml-1 within 24 h at room temperature, when applied at a high concentration. Conclusions: The relatively narrow host range within B. cereus might mean that these phages need to be used as part of a 'cocktail' of phages for biocontrol, but their efficacy for the control of their host in food was demonstrated. Significance and Impact of the Study: This is the first report of biocontrol by phages of B. cereus in food.