仙人掌桿菌選擇性培養基之評估   全文下載

Evaluation of Selective Media for Bacillus cereus

仙人掌桿菌（Bacillus cereus, BC）為食品中毒常見之致病原，其發生率居台灣食品中毒案件之第三位。衛生福利部目前公告之檢驗方法係以甘露糖醇-蛋黃-多粘桿菌素（Mannitol-egg yolk-polymyxin, MYP）培養基進行BC培養，但檢體中的背景菌群亦會於MYP培養基上生長而干擾BC之鑑別；因此，美國食品藥物管理局細菌學分析手冊（Bacteriological Analytical Manual, BAM）已增列使用選擇性培養基Bacara，該培養基可抑制背景菌群生長，進而提升BC之檢測準確性。本研究主要評估選擇性培養基Bacara對BC之檢測效能，包括靈敏度、專一性及回收率，並與MYP培養基作比較。結果顯示：Bacara培養基對BC之檢測靈敏度及專一性與MYP培養基相當，但前者抑制非BC菌株生長之比率（89.1%）明顯高於後者（18.8%），表示Bacara培養基對BC之選擇性優於MYP培養基。當BC分別混合大腸桿菌或沙門氏桿菌培養時，Bacara培養基之BC回收率（94%-103%）與MYP培養基（96%-112%）無顯著差異，但當BC混合金黃色葡萄球菌時，Bacara培養基之BC回收率（100%）明顯高於MYP培養基（69%）（p <0.05），此乃因前者能有效抑制金黃色葡萄球菌而使BC生長不受干擾所致。將BC添加於5種食品基質（保久乳、白米飯、鮭魚炒飯、牛肉及青花菜）後分別培養於MYP及Bacara培養基，其BC回收率分別介於99-127%及104-131%間，兩培養基數值於各食品基質均無顯著差異。綜合以上結果，選擇性培養基Bacara對仙人掌桿菌具有優良的選擇性與檢測能力，且適用於各種食品基質中仙人掌桿菌之檢驗。

Bacillus cereus (BC) is a common foodborne pathogen, ranking third in food poisoning outbreaks in Taiwan. According to the current detection method promulgated by Ministry of Health and Welfare, mannitol-egg yolk polymyxin agar (MYP) is used for culturing BC. However, the concurrent growth of background flora in samples can interfere with the accurate identification of BC. The U.S. FDA Bacteriological Analytical Manual (BAM) has incorporated the use of selective medium Bacara, due to its advantageous inhibitory ability on the growth of background microorganisms and thus improvement of the detection accuracy for BC. In this study, the performance of Bacara medium for detecting BC, including sensitivity, specificity and recovery rate, was evaluated and compared with that of MYP. The sensitivity and specificity of Bacara were found comparable to those of MYP. However, Bacara demonstrated significantly higher selectivity; it inhibited the growth of 89.1% of non-BC strains tested, compared to just 18.8% on MYP. When BC was co-cultured with Echerichia coli or Salmonella Typhimurium in various proportions, there was no significant difference in recovery rates of BC between Bacara (94-103%) and MYP (96-112%). By contrast, co-culture of BC with Staphylococcus aureus led to a significantly lower recovery of BC on MYP (69%) compared to Bacara (100%) (p < 0.05), because the growth of S. aureus was flourishing on MYP but completely inhibited on Bacara. Spiking BC into five food matrices (long-life milk, rice, salmon fried rice, beef and broccoli) and culturing the spiked BC on MYP and Bacara generated BC recovery rates of 99-127% and 104-131%, respectively, with no significant difference between the two media. In conclusion, Bacara medium demonstrated excellent selectivity and was effective in the detection of Bacillus cereus across various food matrices.