| Bacillus cereus is a foodborne pathogen that can cause diarrhea and vomiting syndrome.The bacterium is widespread in nature and often exists in soil,dust and sewage.The food it contaminates is mainly starch-rich foods such as rice and pasta.In addition,it also contaminates vegetables,dairy products,fermented foods and meat,and is one of the main pathogens causing food poisoning in China.Despite advances in modern technology,the food industry still faces the threat of microbial contamination.Overuse of antibiotics has led to the emergence of more and more resistant strains of Bacillus cereus.In addition,the bacteria can produce spores with strong resistance to stress and intestinal toxins that cannot be destroyed by high temperature sterilization.Traditional food sterilization methods gradually show their limitations in the face of increasingly serious food safety problems,and strive to develop new methods to control The contamination of Bacillus cereus in food and food processing environments is very important,so phages have gradually come into sight as a method of natural biological sterilization.In this study,Bacillus cereus was used as the host strain,and a lytic phage was selected from the untreated wastewater of the First Hospital of Jilin University and named BC-T25.Observed by transmission electron microscopy,the phage BC-T25 belongs to the family Long tailed phages of the order Phaephagae.The head of bacteriophage BC-T25 is a regular icosahedron with a diameter of about 94.3 nm.The results of its biological characteristics test showed that the bacteriophage BC-T25 had a short incubation period,strong lytic property,and high stability.The incubation period is 20 min,the lysis period is 40 min,the average outbreak is 930 PFU / cell,the optimal infection multiplicity of bacteriophage BC-T25 is 1,and the bacteriophage BC-T25 has good thermal stability,and can be at temperatures of 50℃ and 60℃.Survival for more than an hour still maintains a high vitality,but it basically losesactivity after 30 minutes in an environment of 70 ℃.The phage BC-T25 also has better acid-base stability,and will only be inactivated when the pH is ≤3 or ≥11.The bacteriophage BC-T25 gene can be cleaved by six restriction endonucleases(HindⅢ、XbaⅠ、SacⅠ、KpnⅠ、EcoRⅤ、NdeⅠ).In this study,the entire genome of phage BC-T25 was sequenced.The sequencing results were uploaded to GenBank with the sequence number MN150686.The bacteriophage BC-T25 genome was 157977 bp in total length,with a GC content of 40.03%,and contained 16 tRNAs.No virulence and drug resistance genes were detected in the genome.The phage BC-T25 genome contains a total of 236 open reading frames(ORFs),of which 203 are forward and 33 are reverse.Among them,there are 42 ORFs presumed to have known functions,and the rest are putative proteins with unknown functions.Evolutionary analysis shows that the phage BC-T25 is very close to the reported phage of Bacillus cereus.This study tested the bactericidal effect of bacteriophage BC-T25 on artificially contaminated fermented foods.The results showed that bacteriophage BC-T25 could effectively inhibit the growth of the host bacteria Bacillus cereus and had no effect on the growth of Bacillus subtilis.At the same time,when single cations Ca2 +,Mg2 +or Ca2 +,Mg2 +,and Na + are mixed,the bacteriostatic effect of phages is improved.Only Na + alone has no obvious antibacterial effect.In summary,this study investigated the biological characteristics and preliminary genome-wide analysis of the isolated Bacillus cereus bacteriophage BC-T25,and it has a good application in inhibiting the contamination of Bacillus cereus in fermented food,and it can be a future food.Prevention and control of safety issues provide some direction and basic data. |
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