Characterization of three autolysins with activity against cereulide-producing Bacillus isolates in food matrices

Bacillus cereus is a pathogen related with diarrhoeal or emetic food poisoning cases, of which the latter caused by the cereulide-producing isolates are more severe with several reported lethal cases. It is therefore necessary to develop an effective strategy to prevent the propagation of B. cereus in the food supply. In this study, three autolysins from the cereulide-producing B. cereus group isolates, LysIS075, LysF8819.1 and LysCER057, were identified and characterized. The results showed that the three autolysins were highly lytic and bactericidal to the tested cereulide-producing B. cereus group strains and cross-lytic against other tested B. cereus group strains, and they could inhibit the spore germination and propagation of their tested derived emetic strains. Physical and chemical characterization showed that all the three autolysins were alkalophilic with the optimal activity at pH 9.0 or 9.5 with one exception of LysF8819.1 also having significant lytic activity at pH 5.0, and they all had relative strong lytic activity at 37-50 °C during the 30 minute assay. However, LysCER057 showed relative susceptibility to thermo-condition. Remarkably, the separate or cock-tail addition of the three autolysins in food matrices (milk and rice porridge) showed effective bactericidal activity within the tested 2 h. All the results revealed that the three autolysins might be potential candidates to control emetic B. cereus strains in different applications.