Supplementation of Modified Mannitol-Yolk-Polymyxin B Agar with Cefuroxime for Quantitative Detection of Bacillus cereus in Food

Paper-based sensor from pyrrolidinyl peptide nucleic acid for the efficient detection of Bacillus cereus

Bacillus cereus is one of the most common foodborne pathogens found in various kinds of staple foods such as rice and wheat. A rapid and accurate detection method for this pathogen is highly desirable for the sustainable production of relevant food products. While several classical and molecular-based detection methods are available for the identification of B. cereus, they suffered one or more limitations such as the requirement for a tedious and time-consuming process, less than ideal specificity, and the lack of portability. Herein, we developed the first paper-based sensing device that exhibits high species specificity with sufficiently low limit of detection for the visual detection of specific DNA sequences of B. cereus. The success is attributed to the strategic planning of fabrication in various dimensions including thorough bioinformatics search for highly specific genes, the use of the pyrrolidinyl peptide nucleic acid (PNA) probe whose selectivity advantage is well documented, and an effective PNA immobilization and DNA-binding visualization method with an internal cross-checking system for validating the results. Testing in rice matrices indicates that the sensor is capable of detecting and distinguishing B. cereus from other bacterial species. Hence, this paper-based sensor has potential to be adopted as a practical means to detect B. cereus in food industries.

Development of a selective and differential media for the isolation and enumeration of Bacillus cereus from food samples

AIM

Identification and enumeration of foodborne pathogens in food stuffs are valuable concerns. In the present study, starch-blood-egg yolk-polymyxin B-trimethoprim-ceftazidime (SBYPTC) agar was established to isolate and specify the number of Bacillus cereus in food products.

METHODS AND RESULTS

The effectiveness of the developed medium in selecting for B. cereus from pure cultures and food matrixes naturally contaminated by high levels of microbiota was estimated, and the results were compared with that of two commercially available MYPA and PMBA media. In pure cultures, there were no significant differences in the recoverability of B. cereus among the three media, however, SBYPTC agar showed a greater exclusivity. To examine SBYPTC performance in food, B. cereus were artificially inoculated into lettuce and potato samples with high background microbiota in two separated experiments. There were no significant differences between MYPA and PEMBA. However, SBYPTC manifested greater selectivity and exclusivity and made the differentiation easier by allowing growth of B. cereus in separated colonies and inhibiting competing microflora.

CONCLUSION

Our results showed that SBYPTC has high selective properties in comparison with MYPA and PEMBA. Thus, it can be considered as a useful tool to monitor the existence and the number of B. cereus in foods especially those contaminated with high levels of microflora.

SIGNIFICANCE AND IMPACT OF THE STUDY

In the food industry, SBYPTC can be employed for food quality assurance to monitor B. cereus in food products contaminated with high levels of microbiota.