Developing a Cas12a-based detection method on the emetic Bacillus cereus strains in infant formulas

Emetic Bacillus cereus is a significant foodborne pathogen typically causing gastrointestinal disorders in adults, but the toxin production and antimicrobial resistance could lead to more severe or even fatal outcomes in infants. Given its emergence in infant foods and the high virulence potential, a rapid and sensitive detection of this significant microbial hazard is urgently required. Here, we developed a Cas12a-based detection method by targeting ces (cereulide toxin synthetase) and gyrB genes of the emetic Bacillus cereus strains. This method effectively differentiated the ces-carried Bacillus cereus strains from other bacteria, achieving a detection limit of 1 CFU/mL for bacterial DNA artificially contaminated in infant formula samples. Furthermore, we collected 146 infant formula products from the market to compare the performance of the Cas12a-based assay, qPCR approach and the traditional culture method. The results revealed that over 80 % of sampled infant formula were Bacillus cereus-positive, 36 % of which were ces-positive. The Cas12a-based assay exhibited a comparable detection rate but with improved efficiency compared to the other two methods. Collectively, the findings not only validate the effectiveness and reliability of the newly-developed detection, but also alert a pressing need for enhanced food safety surveillance in the infant formula industry and timely targeted public health interventions for policymakers.