Study On Risk Assessment And Biofilm-forming Ability Of Foodborne Bacillus Cereus

Bacillus cereus,a common food-borne pathogen,is widespread in water,air,soil and other food-contacting environments.The food poisoning cases caused by B.cereus frequently happen.In order to further investigate the contamination of B.cereus in foods,the potential risk and genetic diversity of 247 B.cereus isolated from edible fungi in the national risk survey conducted previously were performed.Besides,105 B.cereus isolated from pasteurized milk and 247 B.cereus isolated from edible fungi were screened for biofilm-forming ability.The main results are as follows:1.For 247 B.cereus isolated from edible fungi,9 virulence-related genes were detected.All isolates possessed the nheA gene,the detection rates of the two non-hemolysin genes,nheB and nheC,were over 89.9%.The detection rates of hemolysin genes were close to or above 80%.In addition,the detection rate of emetic toxin synthetase gene cesB was 2.8%.The main type of virulence-related genes was hblA-hblC-hblD-nheA-nheB-nheC-cytK-bceT(42.9%).2.The antibiotic susceptibility analysis showed that glycopeptides,tetracyclines and aminoglycosides had inhibitory effects on B.cereus isolates;however,most of the isolates showed resistance to ?-Lactams,ansamycins and sulfonamides.All the isolates presented 28 antibiotic resistance profiles,and 87(35.1%)isolates have multidrug-resistant property.3.Two hundred and forty-seven strains from edible fungi could be divided into 17 groups(Group A to Group Q)when the similarity coefficient was 70% by ERIC-PCR molecular typing.Most of the isolates were distributed into group C,J,and M.Among them,group C was the dominant group with a degree of correlation between ERIC-PCR fingerprint,antibiotic resistance profile,and virulence gene profile.4.Biofilm-forming ability of 105 B.cereus isolated from pasteurized milk was screened by using crystal violet(CV)semi-quantitative assay.The result showed that there were 39 strains with strong biofilm-forming ability.The results of scanning electron microscopy(SEM)and confocal laser scanning microscopy(CLSM)were consistent with the CV test.In addition,the biofilm formation ability of 247 B.cereus isolated from edible fungi were screened by minimal salts glycerol glutamate(MSgg)medium,with which we identified 16 isolates with strong biofilm-forming ability.This study focused on the potential risks and genetic diversity of food-borne B.cereus in China and revealed that the genetic diversity is related to the distribution of virulence genes and antibiotic resistant profiles.We further screened biofilm-forming ability of B.cereus isolated from different food sources and obtained different isolates with distinct ability of biofilm formation.In sum,this study provided the basis for the prevention and risk control of foodborne B.cereus,and the material basis for subsequent investigation on mechanism of biofilm formation.