Development of blood–yolk–polymyxin B–trimethoprim agar for the enumeration of Bacillus cereus in various foods

• We developed blood–yolk–polymyxin B–trimethoprim agar (BYPTA).
• BYPTA is a selective medium for the enumeration of Bacillus cereus (B. cereus) in foods.
• We compared the performances of BYPTA and mannitol–yolk–polymyxin B agar (MYPA).
• No statistical difference was observed in recoverability (p > 0.05).
• BYPTA showed higher selectivity, especially in foods with high background microflora.

Blood–yolk–polymyxin B–trimethoprim agar (BYPTA) was developed by the addition of egg yolk, laked horse blood, sodium pyruvate, polymyxin B, and trimethoprim, and compared with mannitol–yolk–polymyxin B agar (MYPA) for the isolation and enumeration of Bacillus cereus (B. cereus) in pure culture and various food samples. In pure culture, there was no statistical difference (p > 0.05) between the recoverability and sensitivity of MYPA and BYPTA, whereas BYPTA exhibited higher specificity (p < 0.05). To evaluate BYPTA agar with food samples, B. cereus was experimentally spiked into six types of foods, triangle kimbab, sandwich, misugaru, Saengsik, red pepper powder, and soybean paste. No statistical difference was observed in recoverability (p > 0.05) between MYPA and BYPTA in all tested foods, whereas BYPTA exhibited higher selectivity than MYPA, especially in foods with high background microflora, such as Saengsik, red pepper powder, and soybean paste. The newly developed selective medium BYPTA could be a useful enumeration tool to assess the level of B. cereus in foods, particularly with high background microflora.