| Bacillus cereus is group of bacteria that includes species such as B. anthracis, B. mycoides, B. thuringienesis, B. cereus and B. weihenstephanensis, the latter two of which are implicated in food poisoning as well as spoilage of milk. Due to their ability to form spores, the current methods used to control these bacteria in milk mostly involve high heat treatments, which alter the natural composition of the milk. The objective of the present study was to utilize specific lytic bacteriophages as an alternative method to control cells and spores of the B. cereus group in milk. Four strongly lytic phages designated, Bc431 v 1, Bc431 v2, Bc431 v3 and Bc431 v4 (V1, V2, V3 and V4, respectively), were isolated against B. cereusstrains. The four isolated phages demonstrated a very broad host range against members of the B. cereusgroup, including B. anthracis, the causative agent of the fatal human disease, anthrax. Phages V1 and V3 were provisionally characterized as viruses of the Myoviridae family, while phages V2 and V4 were members of the Siphoviridae family. infectivity and stability studies showed that phages V1 and V3 were more stable under different physical and chemical conditions. Genome sequencing analysis further revealed that phage Bc431 v3 (formally named vB_ BceM_Bc431v3) was related to members of "Twort-like viruses." Studies of the interaction between the phage Bc431v3 and B. cereusspores showed that the phage was efficiently adsorbed onto the exosporium layer of the spores; and, that phage DNA was translocated into the spore. The frequency of the phage DNA entrapment in spores was significantly decreased upon suppression of the RNA-polymerase sigma factor B (sigmaB). The application of the phage Bc431v3 in powdered and fresh pasteurized milk successfully inhibited the outgrowth of B. cereusspores and extended the shelf life of milk especially when stored at chilled temperatures. This study suggests that the employment of phage Bc431v3 could be a very promising way to control members of B. cereusgroup in milk without altering its composition. |
