Quantitative Validation of Two Novel Selective Media for the Enumeration of Bacillus cereus in Fermentation Sauce Samples

Introduction: In the previous studies, we developed two novel selective media, Blood-yolk-polymyxin B-trimethoprim agar (BYPTA) and modified mannitol-yolk-polymyxin B agar (mMYPA), for the enumeration of Bacillus cereus (B. cereus) in foods. BYPTA was developed by the addition of egg yolk, laked horse blood, sodium pyruvate, polymyxin B, and trimethoprim, and mMYPA was developed by supplementing mannitol-yolk-polymyxin B agar (MYPA) with trimethoprim.

Purpose: In this study, two novel selective medium were compared with MYPA for the isolation and enumeration of B. cereus in naturally contaminated fermentation sauce samples.

Methods: A total of 46 fermentation sauce samples were purchased from a local retail market. Each sauce sample (25 g) was suspended in 225 ml of Butterfield’s phosphate-buffered water and homogenized for 2 min. Subsequently, 1 ml of homogenate was serially diluted (10-fold) in PBS followed by the inoculation of 0.1 ml of each dilution onto three plating media in duplicate. MYPA and mMYPA were incubated at 30°C and BYPTA plates at 37°C for 24 h.

Results: No statistical difference was observed in the quantitative enumeration (P > 0.05) between three selective media, whereas BYPTA and mMYPA exhibited higher selectivity than MYPA excluding the background flora in fermentation food samples.

Significance: Two novel selective medium could be a useful enumeration tool to assess the level of B. cereus in various fermentation sauce samples.