Environmental and Pathogenic Microbiology Laboratory, School of Environmental and Life Sciences, University of Newcastle, Newcastle, New South Wales, Australia.
PLoS One. 2012;7(1):e29031. doi: 10.1371/journal.pone.0029031. Epub 2012 Jan 24.
The effect of temperature fluctuation is an important factor in bacterial growth especially for pathogens such as the staphylococci that have to remain viable during potentially harsh and prolonged transfer conditions between hosts. The aim of this study was to investigate the response of S. aureus, S. epidermidis, and S. lugdunensis when exposed to low temperature (4°C) for prolonged periods, and how this factor affected their subsequent growth, colony morphology, cellular ultra-structure, and amino acid composition in the non-cytoplasmic hydrolysate fraction. Clinical isolates were grown under optimal conditions and then subjected to 4°C conditions for a period of 8 wks. Cold-stressed and reference control samples were assessed under transmission electron microscopy (TEM) to identify potential ultra-structural changes. To determine changes in amino acid composition, cells were fractured to remove the lipid and cytoplasmic components and the remaining structural components were hydrolysed. Amino acid profiles for the hydrolysis fraction were then analysed for changes by using principal component analysis (PCA). Exposure of the three staphylococci to prolonged low temperature stress resulted in the formation of increasing proportions of small colony variant (SCV) phenotypes. TEM revealed that SCV cells had significantly thicker and more diffuse cell-walls than their corresponding WT samples for both S. aureus and S. epidermidis, but the changes were not significant for S. lugdunensis. Substantial species-specific alterations in the amino acid composition of the structural hydrolysate fraction were also observed in the cold-treated cells. The data indicated that the staphylococci responded over prolonged periods of cold-stress treatment by transforming into SCV populations. The observed ultra-structural and amino acid changes were proposed to represent response mechanisms for staphylococcal survival amidst hostile conditions, thus maintaining the viability of the species until favourable conditions arise again.
温度波动的影响是细菌生长的一个重要因素，特别是对于金黄色葡萄球菌等病原体来说，它们在宿主之间潜在的恶劣和长时间的转移条件下必须保持存活。本研究的目的是研究金黄色葡萄球菌、表皮葡萄球菌和路邓葡萄球菌在长时间暴露于低温（4°C）时的反应，以及这一因素如何影响它们随后的生长、菌落形态、细胞超微结构和非细胞质水解产物部分的氨基酸组成。临床分离株在最佳条件下生长，然后在 4°C 条件下培养 8 周。通过透射电子显微镜（TEM）评估冷应激和参考对照样品，以确定潜在的超微结构变化。为了确定氨基酸组成的变化，细胞被断裂以去除脂质和细胞质成分，剩余的结构成分被水解。然后通过主成分分析（PCA）分析水解产物部分的氨基酸图谱变化。三种葡萄球菌长时间暴露于低温应激导致小菌落变异（SCV）表型的比例不断增加。TEM 显示，SCV 细胞的细胞壁比其相应的 WT 样品明显更厚、更弥散，金黄色葡萄球菌和表皮葡萄球菌都是如此，但路邓葡萄球菌的变化不显著。在冷处理细胞中，结构水解产物部分的氨基酸组成也发生了实质性的种特异性改变。数据表明，葡萄球菌通过转化为 SCV 群体对长时间的冷应激处理做出反应。观察到的超微结构和氨基酸变化被认为代表了葡萄球菌在恶劣条件下生存的反应机制，从而保持了该物种的活力，直到再次出现有利条件。
