重组酶介导的隐孢子虫属特异性等温核酸扩增方法的建立及评价

Establishment and evaluation of the detection method of Cryptosporidium specific DNA fragment by recombinase aided isothermal amplification

目的建立一种可用于隐孢子虫检测的重组酶介导的等温核酸扩增(RAA)方法,并对其检测敏感性和特异性进行评价。方法以隐孢子虫属特异性18S rRNA核酸序列作为检测靶标,采用Amplfix软件设计、合成引物及荧光检测探针,构建并优化RAA荧光反应体系;分别以不同拷贝数的含18S rRNA靶序列的重组质粒、不同浓度隐孢子虫卵囊基因组DNA及不同数量隐孢子虫卵囊基因组DNA为模板进行RAA荧光法检测,以评价其敏感性;分别以隐孢子虫卵囊、蓝氏贾第鞭毛虫包囊、日本血吸虫虫卵、似蚓蛔线虫虫卵、华支睾吸虫虫卵、沙门氏菌、志贺氏菌基因组DNA为模板进行RAA荧光法检测,以评价其特异性。结果成功建立了隐孢子虫检测RAA法,该方法可在39℃、20 min内得到隐孢子虫属18S rRNA基因片段的有效扩增。以不同拷贝数的含18S rRNA靶序列的重组质粒、不同浓度隐孢子虫卵囊基因组DNA及不同数量隐孢子虫卵囊基因组DNA为模板,该方法最低检出限分别为102拷贝/μL、1 pg/μL和1个/50μL;以蓝氏贾第鞭毛虫包囊、日本血吸虫虫卵、似蚓蛔线虫虫卵、华支睾吸虫虫卵、沙门氏菌、志贺氏菌基因组DNA为模板的荧光RAA扩增结果均为阴性。结论成功建立了一种可用于检测隐孢子虫卵囊DNA的RAA法,该方法操作简便、反应快速,敏感性和特异性均较好。

Objective To establish a recombinase-aided isothermal amplification(RAA) assay for detection of Cryptosporidium. Methods Based on Cryptosporidium-specific 18S rRNA selected as the target gene to be detected, and the primer sequences and fluorescent probes designed using the software Amplfix, and a fluorescent RAA assay was established and optimized. The fluorescent RAA assay was performed to detect 18S RNA target sequence-contained recombinant plasmids at various copies, genomic DNA of Cryptosporidium oocysts at various concentrations, and genomic DNA extracted from various numbers of Cryptosporidium oocysts to assess the sensitivity of the assay, and to detect genomic DNA extracted from Cryptosporidium oocysts, Giardia lamblia cysts, Schistosoma japonicum eggs, Ascaris lumbricoides eggs, Clonorchis sinensis eggs, Salmonella and Shigella to determine the specificity of theassay. Results A fluorescent RAA assay was successfully established, which was effective to amplify the specific 18S RNA gene fragments of Cryptosporidium within 20 min at 39 ℃. The lowest limits of the fluorescent RAA assay were 102 copies/μL for detection of 18S RNA target sequence-contained recombinant plasmids at various copies, 1 pg/μL for detection of genomic DNA of Cryptosporidium oocysts at various concentrations, and one Cryptosporidium oocyst/μL for detection of genomic DNA extracted from various numbers of Cryptosporidium oocysts, and the fluorescent RAA assay was all negative for detection of genomic DNAfromG. lamblia cysts, S. japonicum eggs, A. lumbricoides eggs, C. sinensis eggs, Salmonella and Shigella. Conclusion A novel fluorescent RAA assay is successfully established, which is simple, rapid, sensitive and specific to detect genomic DNA of Cryptosporidium oocysts.