Distribution of Bacillus cereus and vomiting toxin gene in cooked rice samples which simulated contaminated by raw vegetables

Abstract

ObjectiveTo analyze the distribution of Bacillus cereus （B. cereus） and vomiting toxin gene （ces） in cooked rice samples which simulated contaminated by raw vegetables， and provide basic data for prevention of food poisoning caused by B.cereus.MethodsFifty raw vegetable samples were collected in this study. Simulate method was as contaminated “freshly cooked rice” with 0.85% physiological saline solution from washing raw vegetables， and then place it in a 30 ℃ 70% RH environment for 24 h to prepare a sample of “contaminated rice”. Plate counting， real time PCR and digital PCR were performed for raw vegetable and “contaminated rice” samples. Statistical analysis was performed on the detection rates grouped by different vegetable types for raw vegetable samples and “contaminated rice” contaminated with them.ResultsThe detection ratios of B.cereus， ces gene and Bac16s RNA gene in raw vegetables was 80.00% （40/50）， 0（0/50） and 10.00%（5/50）. The detection ratios of B.cereus， ces gene and Bac16s RNA gene in “contaminated rice” was 94.00% （47/50）， 14.00% （7/50） and 90.00% （45/50）. There was significant difference in the detection ratio of B.cereus between raw vegetables collected from agricultural markets and farmland（χ2=11.063， P=0.000 88 correction）， and the difference in the detection rates of Bac16s RNA gene and ces genes in “contaminated rice” contaminated with the two groups of raw vegetables mentioned above is statistically significant（χ2=3.926， P=0.047 5 correction； χ2=5.444， P=0.019 6 correction）. Seven “contaminated rice” were tested positive for the ces gene using real time PCR， with Ct values ranging from 24.12 to 37.73， and digital PCR results ranging from 6.8 copes/μL-6.2×106 copes/μL.ConclusionCooked rice samples which simulated contaminated by raw vegetables might be has the etiology characteristics that lead to a risk of food poisoning caused by B.cereus.

Keywords

• bacillus cereus
• rice
• raw vegetables
• vomiting toxin