Isolation and Identification of B. cereus

For B. cereus sl isolation, all the samples were diluted and first chosen according to the National Food Safety Standard Method for Food Microbiological Examination (GB 4789.40-2010) (Gao et al., 2018 (link)). In total, 166 colonies have been picked. These 166 colonies were picked and then placed onto the Mannitol-Yolk Polymyxin Agar Plate (Beijing Land Bridge Technology Co. Ltd., Beijing, China), and then cultured at 30°C for 24 h (Owusu-Kwarteng et al., 2017 (link)). The colonies with pink color (81/166, 48.80%) were selected for further identification.
Identification of B. cereus sl isolates used a polymerase chain reaction (PCR) thermal cycler (Bio-Rad S1000; Bio-Rad, Hercules, CA, USA) via 16S rRNA and panC gene. DNA of B. cereus isolates was extracted with the InstaGene Matrix DNA Extraction Kit (Bio-Rad) following the instructions of Owusu-Kwarteng et al. (2017 (link)). The panC gene analysis was performed using the primers (Sangon, China), and conditions are shown in Supplementary Table S1 with negative and positive (DNA of B. cereus ATCC 11778; China Center of Industrial Culture Collection, Beijing, China) controls.
The PCR products were sequenced by SinoGenoMax Co. Ltd. Then, the sequencing results were BLASTed in the GenBank database (http://www.ncbi.nlm.nih.gov/BLAST/). The degree of homology for the universal 16S rRNA gene and the panC gene was higher than 99%.