Comparison of Sequencing Results between PRRSV ORF5 Amplification Products and Its Cloning
In order to clarify the difference between direct sequencing and post cloning sequencing of PCR products,and verify the“accuracy”of the former,PRRSV ORF5 PCR positive amplified product glue of the tissue samples(A,B)collected from two intensive swine farms were recycled and then connected to pMD19-T vector,15 positive subclone single colonies were respectively taken and sequenced with the original PCR products,then 16 sequences obtained from each sample were compared and analyzed. The results showed that the nucleotide homology between the 16 sequences in the two groups were from 84.2% to 100% and from 87.4% to 100%,respectively,and that of PCR products and their 15 subclone sequences were from 87.7% to 97.3% and from 87.9% to 100%,respectively. For genetic evolution analysis,the sequence of sample A and its subclone sequences were divided into lineages 1,5 and 8,accounting for 6.25%,87.50% and 6.25%,respectively,sample A together with its 12 subclone sequences belonged to lineages 5;sample B and its subclone sequences were divided into lineages 5 and 8,accounting for 68.75% and 31.25%,respectively,sample B together with its 10 subclone sequences belonged to lineages 5. In conclusion,PRRSV ORF5 sequence were diverse in the same sample but with different abundance in different samples. Therefore,direct sequencing of PRRSV ORF5 products by PCR contributed to identifying the prevalent strains within a farm.