Objective       To construct T7 phage display cDNA library from methicillin-resistant Staphylococcus aureus (MRSA) N315 in order to found a basis for screening and identification of regulatory factor of N315 staphylococcal cassette chromosome gene (scc).       Methods       Total RNA was extracted from MRSA N315 by Tripure reagents and digested with DNase Ⅰ to get rid of the contamination of genomic DNA. Then

the total RNA was reverse-transcribed into double-stranded cDNA with random hexamer primers

and subsequently treated with end modification

adaptors ligation

and EcoRⅠ/HindⅢ digestion. After eliminated excess adaptors and small fragments (less than 300 bp)

the cDNA fragment was ligated

into T7Select 10-3 vector. The MRSA N315 phage display cDNA library was constructed by package reaction in vitro and plate proliferation. Plaque assay and PCR amplification were used to evaluate the library.          Results       The total number of primary recombinants was about 1.335×10

6

  pfu

and the phage titer of the amplified library was 3.26×10

10

  pfu/mL. Insert ratio of 24 random plaques was proved to be 100% by PCR amplification

and the length of insert DNA ranged from 300 bp to 1 500 bp.       Conclusion       A T7 phage display cDNA library from MRSA N315 is successfully constructed.