Vargas Susana, Millán-Chiu Blanca E, Arvizu-Medrano Sofía M, Loske Achim M, Rodríguez Rogelio
Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Blvd. Juriquilla 3001, 76230 Querétaro, Qro., Mexico.
CONACyT, - Centro de Física Aplicada y Tecnología Avanzada, Universidad Nacional Autónoma de México, Blvd. Juriquilla 3001, 76230 Querétaro, Qro., Mexico.
J Microbiol Methods. 2017 Jun;137:34-39. doi: 10.1016/j.mimet.2017.04.004. Epub 2017 Apr 9.
A comparison between plate counting (PC) and dynamic light scattering (DLS) is reported. PC is the standard technique to determine bacterial population as a function of time; however, this method has drawbacks, such as the cumbersome preparation and handling of samples, as well as the long time required to obtain results. Alternative methods based on optical density are faster, but do not distinguish viable from non-viable cells. These inconveniences are overcome by using DLS. Two different bacteria strains were considered: Escherichia coli and Staphylococcus aureus. DLS was performed at two different illuminating conditions: continuous and intermittent. By the increment of particle size as a function of time, it was possible to observe cell division and the formation of aggregates containing very few bacteria. The scattered intensity profiles showed the lag phase and the transition to the exponential phase of growth, providing a quantity proportional to viable bacteria concentration. The results revealed a clear and linear correlation in both lag and exponential phase, between the Log(colony-forming units/mL) from PC and the Log of the scattered intensity I from DLS. These correlations provide a good support to use DLS as an alternative technique to determine bacterial population.
本文报道了平板计数法（PC）与动态光散射法（DLS）的比较。平板计数法是确定细菌数量随时间变化的标准技术；然而，该方法存在缺点，例如样品制备和处理繁琐，以及获得结果所需时间长。基于光密度的替代方法更快，但无法区分活细胞和死细胞。使用动态光散射法克服了这些不便之处。研究考虑了两种不同的细菌菌株：大肠杆菌和金黄色葡萄球菌。动态光散射法在两种不同的光照条件下进行：连续光照和间歇光照。通过观察粒径随时间的增加，可以观察到细胞分裂以及含有极少量细菌的聚集体的形成。散射强度曲线显示了生长的延迟期和向指数生长期的转变，提供了与活细菌浓度成比例的量。结果表明，在延迟期和指数生长期，平板计数法测得的每毫升菌落形成单位的对数（Log(colony-forming units/mL)）与动态光散射法测得的散射强度I的对数之间存在明显的线性相关性。这些相关性为将动态光散射法用作确定细菌数量的替代技术提供了有力支持。
