Traceability Of Bacillus Cereus In Raw Milk And Research On Its Protease Production Characteristics

With the slogan "a cup of milk,a strong nation",milk has become an indispensable part of the daily diet of people of all ages,and its safety will naturally receive more and more attention.Bacillus cereus is one of the main pathogenic microorganisms that contaminate raw milk.It can produce spores under extreme conditions that are not conducive to the reproduction of microorganisms,and can be contaminated to milk and dairy products through a variety of ways.Moreover,the thermostable protease produced by B.cereus can decompose the protein in milk and reduce the quality of milk.In order to determine the type,source and spoilage ability of B.cereus in raw milk,this study used 18 raw milk samples collected from a ranch in Tianjin and 82 environmental samples as the research object,using culture method,biochemical identification and polymerase chain reaction(PCR)to isolate and identify 47 B.cereus;14 sequence types(ST)were obtained using MLST typing method,of which 5 STs are new;using BioNumerics software to trace the source of B.cereus in raw milk,it was found to be isolated from raw milk The main sequence types of ST1150 are related to feces,air,drinking water,nipple skin,milk cups,and medicated bath cups,indicating that B.cereus is ubiquitous in the environment;PCR was used to determine that B.cereus carries enterotoxin genes(hblA,hblC,Hbl D,nheA,nheB,nheC,cyt K)and cereloid synthase genes(cesB),13 virulence gene carrying modes were found;the protease activity of B.cereus and the 4 heat treatments Heat resistance under the combination,it was found that42 strains of B.cereus remained active under the combination of 55?,5min and 95?,5min heat treatment;under the combination of 121?,10 s heat treatment,there were 9strains(21.43%)of B.cereus Inactivation;21 strains(50%)of B.cereus were inactivated under the heat treatment combination of 5-8s at 135?,indicating that B.cereus has great spoilage potential.