Department of Food Science, University of Otago, PO Box 56, Dunedin 9054, New Zealand.
Department of Food Science, University of Otago, PO Box 56, Dunedin 9054, New Zealand; Riddet Institute, Palmerston North, New Zealand.
Food Res Int. 2019 Feb;116:578-585. doi: 10.1016/j.foodres.2018.08.076. Epub 2018 Aug 27.
Bacillus cereus spores in food are able to survive pasteurization, and if conditions are favourable, subsequently germinate, grow and produce toxins causing food poisoning. The objectives of this study were to firstly determine the impact of cold storage and ion uptake on the thermal resistance of B. cereus spores and secondly to use differential gene expression to help elucidate possible molecular mechanisms for the changes detected in their thermal resistance. B. cereus spores were held at 4 °C in either 0.05 or 0.5 M solutions of cations (Na, Ca Mg,K, Zn) for 6 days and their D-values were estimated. In the presence of sodium chloride (0.05 and 0.5 M), sodium phosphate buffer, (pH 7, 0.05 and 0.5 M) or zinc acetate (0.05 M), D values decreased by 8.8, 10.9, 11.2, 12.9, and 10.2 min respectively, with no evidence of germination (plating methods). Exposure of spores to Na in sodium phosphate buffer (pH 7, 0.05 and 0.5 M) or sodium chloride (0.05 and 0.5 M) resulted in the accumulation of Na (66.0 ± 2.9, 193.1 ± 4.6, 136.2 ± 9.9 and 70.5 ± 2.7 μg/g) by spores at the significant expense of K (10.8 ± 0.5, 7.5 ± 0.2, 8.1 ± 0.4 and 3.6 ± 0.4 μg/g respectively). The mechanism behind the loss of resistance in sodium phosphate buffer (0.05 M) was further investigated by monitoring the differential gene expression using mRNA sequencing. Genes encoding for uracil permease (BC_3890), Mg P-type ATPase-like protein (BC_1581), ABC transporter ATP-binding protein (BC_0815), and 2-keto-3-deoxygluconate permease (BC_4841) were significantly (FDR value ≤0.05) upregulated. This upregulation indicated a possible increase in permeability, which is suggested to account for the increased uptake of sodium ions and the reduction measured in the spore's thermal resistance. This data suggests that during storage at 4 °C in the presence of sodium ions, spores should not be considered to be completely dormant.
食品中的蜡样芽胞杆菌孢子能够耐受巴氏杀菌，如果条件适宜，随后会发芽、生长并产生毒素，导致食物中毒。本研究的目的首先是确定冷藏和离子摄取对蜡样芽胞杆菌孢子耐热性的影响，其次是利用差异基因表达来帮助阐明耐热性检测到的变化的可能分子机制。将蜡样芽胞杆菌孢子在 4°C 下分别置于 0.05 或 0.5 M 的阳离子（Na、Ca、Mg、K、Zn）溶液中保存 6 天，并估计其 D 值。在存在氯化钠（0.05 和 0.5 M）、磷酸钠缓冲液（pH 7，0.05 和 0.5 M）或醋酸锌（0.05 M）的情况下，D 值分别降低了 8.8、10.9、11.2、12.9 和 10.2 分钟，没有发芽的证据（平板计数法）。孢子暴露于磷酸钠缓冲液（pH 7，0.05 和 0.5 M）或氯化钠（0.05 和 0.5 M）中的 Na 导致 Na 的积累（66.0±2.9、193.1±4.6、136.2±9.9 和 70.5±2.7μg/g），以牺牲 K 为代价（10.8±0.5、7.5±0.2、8.1±0.4 和 3.6±0.4μg/g）。进一步通过使用 mRNA 测序监测差异基因表达，研究了在磷酸钠缓冲液（0.05 M）中抗性丧失的机制。编码尿嘧啶渗透酶（BC_3890）、Mg P 型 ATP 酶样蛋白（BC_1581）、ABC 转运体 ATP 结合蛋白（BC_0815）和 2-酮-3-脱氧葡萄糖酸渗透酶（BC_4841）的基因显著上调（FDR 值≤0.05）。这种上调表明通透性可能增加，这表明钠离子的摄取增加，并且测量到的孢子耐热性降低。该数据表明，在 4°C 下储存时存在钠离子，不应认为孢子完全处于休眠状态。
