冷冻胁迫下金黄色葡萄球菌的亚致死及失活规律

Sublethal Injury and Inactivation of Staphylococcus aureus under Freezing Stress

研究-18℃冷冻贮藏、反复冻融和模拟冷链流通下金黄色葡萄球菌的总活性细胞数目、未受损伤细胞数目以及亚致死率的变化,从而了解冷链流通过程中金黄色葡萄球菌的存在状态。结果表明:-18℃冻藏时,随着贮藏时间的增加,金黄色葡萄球菌总活性细胞数目逐渐减少,亚致死率逐渐升高,但在冻藏56d后活细胞下降速率明显变缓,说明亚致死细胞具有较强的抗冷冻胁迫能力。在反复冻融条件下,总活性细胞数目和未受损伤细胞数目均有所增加,亚致死率降低,在模拟食品冷链的温度波动条件下,总活性细胞数目明显减少,但未受损细胞数目随着温度的变化而有所波动。说明了亚致死状态是金黄色葡萄球菌冷冻失活的中间过渡状态,在适宜的温度条件下,亚致死细胞会快速恢复为正常状态。这种不可避免的温度波动造成的亚致死修复,以及亚致死细胞的抗冷冻调节能力可能都是冷链流通过程速冻食品中金黄色葡萄球菌屡屡检出的重要原因。

With the purpose of understanding the existence of Staphylococcus aureus during cold chain circulation, the total number of viable cells and the number of non-injured cells as well as sublethal rate under -18 ℃ storage, freeze-thaw cycle and a simulated cold chain were determined in the present study. As shown by our results, when S. aureus ATCC6538 was frozen and stored at -18 ℃, the total number of viable cells revealed a gradual reduction along with an increase in sublethal rate, but the number of viable cells declined at a markedly lower rate after 56 d of storage, suggesting a potent freezing stress resistance of cells with sublethal injury. In contrast, an obvious increase in total number of viable and noninjured cells together with a decrease in sublethal rate was observed, when S. aureus cells were subjected to 0.5 h freeze-thaw treatment. Under the condition of temperature fluctuation-induced food cold chain, although the total viable cell number decreased during the circulation process, the non-injured cell number fluctuated with temperature. It could be concluded from the present study that the sublethal state was an intermediate transition state of S. aureus during inactivation, and could be rapidly recovered under a suitable temperature. Moreover, the recovery of sublethal cells due to inevitable temperature fluctuation during cold chain circulation, along with the regulation capability of sublethal injured cells against freezing stress might have a close relationship with frequent detection of S. aureus in quick-frozen food.