Selectivity of Mannitol-Yolk-Polymyxin B Agar When Supplemented With Cefsulodin for Enumeration of Bacillus cereus in Food

초록

Bacillus cereus is a foodborne pathogen frequently found in ready-to-eat and minimally processed foods, particularly those that do not undergo heat treatments. Detection techniques for B. cereus are often hampered by abundant background microbiota in complex food matrices such as fermented products and fresh-cut vegetables. Such methodological limitations require the development of more selective supplements. In this study, we aimed to assess mannitol-yolk-polymyxin B agar (MYPA) supplemented with cefsulodin (CEFS-MYPA), a beta-lactam antibiotic. Supplementation with 16 mu g/mL of cefsulodin did not inhibit the growth of B. cereus/B. thuringiensis strains, validating this concentration as optimal for balancing selectivity and recoverability. CEFS-MYPA was applied to seven types of foods for which quantitative B. cereus criteria exist-red pepper powder, soybean paste, strawberry juice, rice porridge, fresh-cut vegetable, sushi, and saengsik artificially inoculated with B. cereus and B. thuringiensis strains. Compared to MYPA, CEFS-MYPA significantly improved B. cereus recovery in red pepper powder (p < 0.05) and showed comparable or slightly enhanced performance in other foods. CEFS-MYPA effectively reduced acid-induced color masking caused by mannitol-fermenting competitors, preserving pH stability and enhancing visual clarity of lecithinase-positive colonies. Background overgrowth was markedly reduced in several samples, except for fresh-cut vegetables, in which competing flora was insufficiently suppressed. These findings highlight the potential of cefsulodin as a selective supplement for enhancing MYPA performance in diverse food matrices. CEFS-MYPA selectivity was especially enhanced for fermented and spice-rich matrices and warrants further investigation in combination strategies for complex food systems. Practical Applications This study offers a practical tool for improving the detection of Bacillus cereus in complex food products such as fermented foods and ready-to-eat foods. The newly formulated CEFS-MYPA medium containing cefsulodin enhances colony visibility and reduces interference from background microorganisms without affecting target recovery. This approach can be readily adopted by food safety laboratories and quality-control facilities to achieve more accurate monitoring of B. cereus contamination in ready-to-eat and minimally processed foods, thereby supporting safer food production and regulatory compliance.

키워드