Quantitative Validation of Two Novel Selective Media for the Enumeration of Bacillus cereus in Naturally Contaminated Fermented Sauce Samples

We compared two novel selective media, blood–yolk–polymyxin B–trimethoprim agar (BYPTA) and modified mannitol–yolk–polymyxin B agar (mMYPA), with mannitol–yolk–polymyxin B agar (MYPA) for the isolation and enumeration of Bacillus cereus in naturally contaminated Korean fermented sauce samples such as red pepper paste, soybean paste, ssamjang and chunggukjang. A total of 81 fermented sauce samples were purchased from a local retail market in Seoul, South Korea. No statistical differences were observed in quantitative enumeration and isolation rates (P > 0.05) among the three selective media. However, BYPTA and mMYPA exhibited higher selectivity than MYPA in excluding the background microflora. In addition, BYPTA (22/81, 27%) and mMYPA (21/81, 26%) detected more fermented sauces with unacceptable levels of B. cereus than MYPA (16/81, 20%) suggesting that the two novel selective media could be used to efficiently detect unacceptable levels of B. cereus in Korean fermented sauce. The two novel selective media could be powerful tools to enumerate the level of B. cereus in fermented sauce samples that have a high level of background microflora. Practical Applications In previous studies, we developed two novel selective media, BYPTA and mMYPA for the enumeration of Bacillus cereus in foods. It is well known that naturally fermented Korean soybean sauces are commonly contaminated with B. cereus, and a high level of background microflora in these foods could behave competitively during the detection of B. cereus. These sauces are also commonly consumed without additional heat treatment. Therefore, highly specific and sensitive media for the enumerative detection of B. cereus in the fermented sauces are needed. In this study, we found that the two novel selective media exhibited greater selectivities and isolation capabilities for B. cereus in the fermented sauces than MYPA. In addition, BYPTA and mMYPA detected more fermented sauces with unacceptable levels of B. cereus than MYPA. We recommend these two media be used in food manufacturing plants and food safety authorities to monitor B. cereus in fermented sauces that have a high level of background microflora.