A Visualized Isothermal Amplification Method for Rapid and Specific Detection of Emetic and Non-emetic Bacillus cereus in Dairy Products

Bacillus cereus is widely distributed in foods, especially dairy products, and can lead to diarrhea (non-emetic B. cereus) and emesis (emetic B. cereus). Although diarrhea due to B. cereus is usually mild, emesis can lead to acute encephalopathy and even death. To develop rapid and sensitive detection methods for B. cereus in foods, specific primers targeting the gyrase B (gyrB) and cereulide synthetase (ces) genes were designed and screened using recombinase polymerase amplification (RPA). Probes and base substitutions were introduced to improve specificity and eliminate primer-dependent artifacts. The 5′ ends of the reverse primers and probes were modified with biotin and fluorescein isothiocyanate for detection of RPA products on a lateral flow strip (LFS). The developed RPA-LFS assay allows detection within 20 min at 37°C with no cross-reactivity with other foodborne pathogens. The limit of detection was 10(4) copies/ml and 10(2) CFU/ml in pure cultures and milk, respectively. Comparisons with established methods using cream obtained similar results. A specific, rapid, and sensitive RPA-LFS assay was successfully developed for on-site detection of B. cereus in dairy products to distinguish emetic from non-emetic strains.