基于TaqMan qPCR检测凡纳滨对虾样品中虾肝肠胞虫并样检测方法的评价

Evaluation on the detection of Enterocytozoon hepatopenaei in pooled DNA samples of Litopenaeus vannamei based on TaqMan qPCR

中文关键词: 凡纳滨对虾  虾肝肠胞虫(EHP)  qPCR  并样检测

英文关键词: Litopenaeus vannamei  Enterocytozoon hepatopenaei (EHP)  qPCR  Pooled sample detection

中文摘要:

      对山东海阳和潍坊的2个养殖凡纳滨对虾群体取样，采用TaqMan qPCR逐尾检测肝胰腺中的虾肝肠胞虫(Enterocytozoon hepatopenaei, EHP)载量，再将提取的DNA样品按5并1(5∶1)、25并1(25∶1)、50并1(50∶1)、100并1(100∶1)和150并1(150∶1)进行并样，检测并样的EHP载量。设定不同临界循环数为假定灵敏度，定性判断各单尾检测阳性及并样组阳性，比较不同并样模式与检测阳性率、诊断灵敏度、诊断特异性等之间的关系以及定量的准确性。结果表明，检测灵敏度过低，会降低高并样率检测的准确性；阳性率在30%以上时，高并样率的检测结果与单样品检测相符性很好；高载量感染的阳性率不低于6.7%时，50∶1以内的并样能准确得出检测结果；低载量感染的阳性率不低于16%时，25∶1以内的并样能得出较好结果；高载量感染的1.3%阳性率和低载量感染的8%阳性率可能导致所有并样出现假阴性结果；各种并样模式均有很好的诊断特异性，50∶1并样的诊断灵敏度与OIE标准推荐的5∶1并样的接近；各并样检测的EHP载量与单样品检测平均值之比在0.27~2.83范围，二者存在极显著相关性，各种并样模式的定量检测结果在数量级水平能大致反映样品的平均EHP载量。本研究为水生动物疫病诊断和流行病学调查的样品检测提供了参考依据。

英文摘要:

      Two populations of Litopenaeus vannamei from Haiyang and Weifang in Shandong Province were sampled. TaqMan qPCR was used to measure Enterocytozoon hepatopenaei (EHP) in the shrimp hepatopancreas one by one, and then the extracted DNA samples were pooled by 5-pool (5∶1), 25-pool (25∶1), 50-pool (50∶1), 100-pool (100∶1), and 150-pool (150∶1) to test the EHP in the pooled samples. The amplification used a special threshold cycle value (Ct) of samples lower/higher than an assumed critical cycle value (Ca), differentiated as an analyzed positive/negative ratio in the single sample test and pooled sample test. The relationship between different pooling modes and the analyzed positive rate, diagnostic sensitivity, diagnostic specificity, and quantitative accuracy were compared. The results showed that the detection for high pooling rate samples could be reduced in very low analytic sensitivity. When the positive rate of individuals in the pooled samples was above 30%, the detection results of the high pooling rate were consistent with that of the single sample detection. If the positive rate of individuals with heavy infections in the pooled sample were not less than 6.7%, satisfying results could be obtained in the sample with a pooling rate below 50∶1; while the positive rate of individuals with light infections in the pooled sample were not less than 16%, the satisfying result could be obtained in the sample with a pooling rate below 25∶1. The pooled samples with a positive rate below 1.3% of individuals with heavy infection, or a positive rate below 8% of individuals with light infection, might lead to false negative results in all pooling rates. All of the pooling modes have good diagnostic specificity. The sample with a 50∶1 pooling rate had a similar diagnostic sensitivity to the sample with a 5∶1 pooling rate, which is the highest pooling rate recommended by the OIE standard. It had a very significant correlation between the mean of the detected EHP load of pooled sample, and the mean of the known EHP load calculated according to the single sample, with a ratio of 0.27~2.83. The quantitative test results of the pooled samples could roughly reflect the average EHP load of the single sample at the order of magnitude. This study provides a reference for sample detection in aquatic animal disease diagnosis, and epidemiological investigations.