Virology Division, Department of Laboratory Medicine, University of Washington, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA
Vaccine and Infectious Diseases Division, University of Washington, Fred Hutchinson Cancer Research Center, Seattle, Washington, USA.
J Clin Microbiol. 2018 Nov 27;56(12). doi: 10.1128/JCM.01061-18. Print 2018 Dec.
An element essential for PCR detection of microbial agents in many sample types is the extraction step, designed to purify nucleic acids. Despite the importance of this step, yields have not been extensively compared across methods to determine whether the method used contributes to quantitative differences and the lack of commutability seen with existing clinical methods. This may in part explain why plasma and blood viral load assays have proven difficult to standardize. Also, studies have identified small DNA fragments of <200 bp in plasma (cell-free DNA [cfDNA]), which may include significant quantities of viral DNA. Our study evaluated extraction yields for 11 commercially available extraction methods, including 4 new methods designed to isolate cfDNA. Solutions of DNA fragments with sizes ranging from 50 to 1,500 bp were extracted, and then the eluates were tested by droplet digital PCR to determine the DNA fragment yield for each method. The results demonstrated a wide range of extraction yields across the variety of methods/instruments used, with the 50- and 100-bp fragment sizes showing especially inconsistent quantitative results and poor yields of less than 20%. Slightly higher, more consistent yields were seen with 2 of the 4 circulating cell-free extraction kits. These results demonstrate a significant need for further evaluation of nucleic acid yields across the variety of extraction platforms and highlight the poor extraction yields of small DNA fragments by existing methods. Further work is necessary to determine the impact of this inconsistency across instruments and the relevance of the low yields for smaller DNA fragments in clinical virology testing.
对于许多样本类型的微生物检测,聚合酶链反应(PCR)检测的一个关键要素是提取步骤,旨在纯化核酸。尽管这一步骤非常重要,但尚未广泛比较各种方法的产量,以确定所使用的方法是否会导致定量差异,以及现有临床方法缺乏可互换性。这可能部分解释了为什么血浆和血液病毒载量检测难以标准化。此外,研究已经在血浆中发现了小于 200 bp 的小 DNA 片段(无细胞 DNA [cfDNA]),其中可能包含大量病毒 DNA。我们的研究评估了 11 种市售提取方法的提取产量,包括 4 种新设计用于分离 cfDNA 的方法。提取大小在 50 到 1500 bp 之间的 DNA 片段溶液,然后通过液滴数字 PCR 测试洗脱液,以确定每种方法的 DNA 片段产量。结果表明,各种方法/仪器的提取产量差异很大,50bp 和 100bp 片段大小的定量结果尤其不一致,产量低于 20%。4 种循环无细胞提取试剂盒中的 2 种试剂盒的产量略高且更一致。这些结果表明,需要进一步评估各种提取平台的核酸产量,突出了现有方法对小 DNA 片段提取产量低的问题。需要进一步研究来确定这种不一致性对不同仪器的影响,以及较小 DNA 片段低产量对临床病毒学检测的相关性。