Comparative genomic analysis of ST239-spa t037 MRSA and ST239-spa t030 MRSA
Objective To identify critical genes in evolution of Staphylococcus aureus (S.aureus).Methods A total of 2457 genes from two whole genomes of S.aureus strains were amplified for fabricating whole genome microarray,which was employed for comparative genome hybridization (CGH) analysis of 23 strains of divergent MRSA clones,including ST239-spa t037 and ST239-spa t030.Representatives of differential genes were confirmed by PCR.Results Four gene clusters were identified to be associated with evolution of major epidemic MRSA clones.The four gene clusters were specific to ST239-spa t030,and belonged to three known genomic islands (vSa4,prophage ΦSa1 and ΦSa3).Eight genes were variable expressed in ST239-spa t030 MRSA from different coutries.Conclusion The acquisition of genomic islands vSa4,prophage ΦSa1 and ΦSa3 enhanced the virulence and resistance of ST239-spa t030 MRSA,and contributed to its rapid replacement of ST239-spa t037 MRSA in China. 
 
Key words: 
Methicillin-resistant S. aureus;  Comparative genomic hybridization;  Genomic island; Evolution