Research On The Contamination Of Bacillus Cereus In Wet Rice Products And Starch Products And The Virulence And Growth Inhibition Of Isolates

Background and ObjectiveThere have been several cases of microbial food poisoning in wet rice products and starch products.Bacillus cereus,which is common in rice and starch products,can cause vomiting and diarrhoeal poisonings and may not be inhibited by ordinary cleaning procedures due to its spore production and biofilm formation ability.In this study,Bacillus cereus in fresh wet rice and starch products was chose as the research object to explore its contamination and pathogenicity,combined with the characteristics of growth and proliferation and the inhibiting effect of four food addictives,in order to provide data for quantitative risk assessment and control measures of Bacillus cereus in wet rice products and starch products.MethodsQuantitative detection and identification of Bacillus cereus in wet rice products and starch products,rice and starch in Guangzhou was carried out.The virulence characteristics of Bacillus cereus strains were analyzed by multiplex PCR and crystal violet staining.The minimum inhibitory concentration(MIC)of four food additives to Bacillus cereus was detected by broth dilution method.The compound test was carried out to study the inhibitory effect of different food additives on Bacillus cereus growth.Results1.The contamination rate of Bacillus cereus in wet rice products and starch products on sale was 43.17%(60/139),and there was no difference between different quarters.The rate of exceeding threshold in food on sale was 3.60%(5/139).The Bacillus cereus contamination rate of the food in the production stage was 50.00%(16/32),and there was no difference in the contamnition situation between stages of production and sale.The Bacillus cereus contamination rates of rice,wheat starch and corn starch were 93.75%(30/32)、70.59%(12/17)and 66.67%(2/3)respectively,suggesting that raw materials may be the main contamination sources of Bacillus cereus.2.A total of 102 Bacillus cereus strains were collected.2.94%of the 102 Bacillus cereus strains carried vomiting toxin gene cesB,all of which came from food.The main enterotoxin virulence genes were nheC(82.35%),bceT(75.49%)and entFM(84.31%),suggesting that all the strains had high causing diarrhoeogenic capacity.The proportion of strong,medium and weak biofilm-forming ability of Bacillus cereus strains was 35.29%,26.47%and 38.24%respectively.Among the vomiting strains,1 strain had strong and 2 strains had weak biofilm-forming ability.3.Dehydroacetic acid and its sodium salts had no inhibitory effect on Bacillus cereus.The MIC of citric acid,ε-polylysine(ε-PL)and nisin against Bacillus cereus were 1.0 mg/mL,0.050 mg/mL and 0.075 mg/mL.The optimal combination was 0.025 mg/mL ε-PL,0.038 mg/mL nisin and 0.125 mg/mL citric acid.Conclusions1.The contamination of Bacillus cereus in wet rice products and starch products should was serious.Under the premise of the current industry rectification,the sales environment did not show an effect on it.Rice and starch may be the sources of Bacillus cereus.2.Foodborne Bacillus cereus strains were at risk of vomiting and diarrhoeal food poisoning.Strains are highly likely to attach and increase virulence in production equipment.3.Dehydroacetic acid and its sodium salt had almost no inhibitory effect on Bacillus cereus.Citric acid,ε-polylysine hydrochloride and nisin had good inhibitory effect on Bacillus cereus,and the superiorly performed mixture systems were selected.