Natural transformation allows transfer of SCCmec-mediated methicillin resistance in Staphylococcus aureus biofilms

Abstract SCC mec is a large mobile genetic element that includes the mecA gene and confers resistance to β-lactam antibiotics in methicillin-resistant Staphylococcus aureus (MRSA). There is evidence that SCC mec disseminates among staphylococci, but the transfer mechanisms are unclear. Here, we show that two-component systems mediate the upregulation of natural competence genes in S. aureus under biofilm growth conditions, and this enhances the efficiency of natural transformation. We observe SCC mec transfer via natural transformation from MRSA, and from methicillin-resistant coagulase-negative staphylococci, to methicillin-sensitive S. aureus . The process requires the SCC mec recombinase genes ccrAB , and the stability of the transferred SCC mec varies depending on SCC mec types and recipients. Our results suggest that natural transformation plays a role in the transfer of SCC mec and possibly other mobile genetic elements in S. aureus biofilms.