Applied Microbiology, Lund Institute of Technology, Lund University, Lund, Sweden.
BMC Microbiol. 2010 May 20;10:147. doi: 10.1186/1471-2180-10-147.
The effects of acetic acid, a common food preservative, on the bacteriophage-encoded enterotoxin A (SEA) expression and production in Staphylococcus aureus was investigated in pH-controlled batch cultures carried out at pH 7.0, 6.5, 6.0, 5.5, 5.0, and 4.5. Also, genomic analysis of S. aureus strains carrying sea was performed to map differences within the gene and in the temperate phage carrying sea.
The sea expression profile was similar from pH 7.0 to 5.5, with the relative expression peaking in the transition between exponential and stationary growth phase and falling during stationary phase. The levels of sea mRNA were below the detection limit at pH 5.0 and 4.5, confirmed by very low SEA levels at these pH values. The level of relative sea expression at pH 6.0 and 5.5 were nine and four times higher, respectively, in the transitional phase than in the exponential growth phase, compared to pH 7.0 and pH 6.5, where only a slight increase in relative expression in the transitional phase was observed. Furthermore, the increase in sea expression levels at pH 6.0 and 5.5 were observed to be linked to increased intracellular sea gene copy numbers and extracellular sea-containing phage copy numbers. The extracellular SEA levels increased over time, with highest levels produced at pH 6.0 in the four growth phases investigated. Using mitomycin C, it was verified that SEA was at least partially produced as a consequence of prophage induction of the sea-phage in the three S. aureus strains tested. Finally, genetic analysis of six S. aureus strains carrying the sea gene showed specific sea phage-groups and two versions of the sea gene that may explain the different sea expression and production levels observed in this study.
Our findings suggest that the increased sea expression in S. aureus caused by acetic acid induced the sea-encoding prophage, linking SEA production to the lifecycle of the phage.
本研究旨在探讨在 pH 值分别为 7.0、6.5、6.0、5.5、5.0 和 4.5 的 pH 控制批次培养中，常见食品防腐剂乙酸对金黄色葡萄球菌噬菌体编码肠毒素 A（SEA）表达和产生的影响。此外，还对携带 sea 基因的金黄色葡萄球菌菌株进行了基因组分析，以绘制该基因和携带 sea 的温和噬菌体中的差异图谱。
SEA 的表达谱在 pH 值为 7.0 至 5.5 之间相似，相对表达量在指数生长和稳定生长阶段之间的过渡时达到峰值，并在稳定生长阶段下降。在 pH 值为 5.0 和 4.5 时，SEA 水平非常低，低于检测限，证实了这一点。与 pH 值为 7.0 和 6.5 相比，在过渡阶段，SEA 基因相对表达水平在 pH 值为 6.0 和 5.5 时分别高出 9 倍和 4 倍，而在指数生长阶段仅观察到相对表达略有增加。此外，在 pH 值为 6.0 和 5.5 时，sea 表达水平的增加与细胞内 sea 基因拷贝数和细胞外含 sea 噬菌体拷贝数的增加有关。SEA 水平随时间推移而增加，在所研究的四个生长阶段中，在 pH 值为 6.0 时产生的水平最高。使用丝裂霉素 C 验证了 SEA 的产生至少部分是由于在测试的三个金黄色葡萄球菌菌株中，sea 噬菌体的前噬菌体诱导所致。最后，对携带 sea 基因的 6 株金黄色葡萄球菌菌株进行了遗传分析，结果显示了特定的 sea 噬菌体群和两个版本的 sea 基因，这可能解释了本研究中观察到的不同 sea 表达和产生水平。
我们的研究结果表明，乙酸引起的金黄色葡萄球菌中 sea 表达增加诱导了携带 sea 的噬菌体，将 SEA 产生与噬菌体的生命周期联系起来。
