Development of selective medium for rapid pre-enrichment of Bacillus cereus from infant formula powder

Bacillus cereus spores frequently contaminate powdered infant formula (PIF) and endanger infant health. Conventional ISO-recommended polymyxin B enrichment broth inhibits trace target spores, while Mannitol Egg Yolk Polymyxin (MYP) and molecular detection need prolonged incubation. This study adopted Plackett-Burman design and Box-Behnken response surface methodology to optimize liquid basal nutrients. Optimized medium increased 6 h viable counts of B. cereus by 37% over commercial medium. After screening five antibacterial agents, 1.0 mg/100 mL ceftazidime was selected. It completely suppresses Escherichia coli, Cronobacter sakazakii and Salmonella Typhimurium, with over 70% recovery for four B. cereus strains under <10 colony-forming units (CFU) low inoculation. Artificial milk powder spiking tests verified its superiority to standard polymyxin-TSB. All isolated colonies obtained Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) identification scores above 2.00. The newly developed 6-h selective pre-enrichment medium is fully applicable to the rapid pre-enrichment pretreatment of samples, providing an efficient and rapid pretreatment strategy for microbial safety monitoring of powdered infant formula.