The transfer of SCCmec among staphylococci.
SCCmec is staphylococcal genomic island which often contains mecA gene conferring resistance to methicillin and all beta-lactam antibiotics. MRSA (methicillin resistant S. aureus) arise from sensitive S. aureus by horizontal transfer of SCCmec from other MRSA and, probably, other staphylococcal species. The first step in the transfer of SCCmec is its excision by site-specific recombinase ccr found on the island itself. Many questions about the transfer mechanism and fitness costs of SCCmec remain open. We are tackling these questions by a variety of approaches such as: study of expression of ccr by promoter fusion in various genetic backgrounds and environmental conditions; monitoring the rate of excision of SCCmec by qPCR; comparison of intact insertion sites among diverse strains; fitness essays to measure the cost of carrying SCCmec.
Comparative genomics of S. aureus.
We have conducted an extensive survey S. aureus isolates from nasal carriage of healthy humans, nasal carriage from cattle farmers and the mastitis isolates from cows. We have assessed the genetic diversity as well as transmission rates of S. aureus strains among different hosts. We have found that certain S. aureus strains have recently undergone genetic modification that prevents them from colonizing humans. Genomic microarrays and whole genome sequencing are currently used to characterize this modification and thus identify the genetic determinants necessary for colonization of humans.