Related Clones Containing SCC mec Type IV Predominate among Clinically Significant Staphylococcus epidermidis Isolates

Abstract

SCC mec is a mobile genetic element that carries the gene ( mecA ) mediating methicillin resistance in staphylococci. For Staphylococcus aureus , four SCC mec types have been described, one (type IV) of which has been associated with newly identified community-acquired methicillin-resistant S. aureus . However, the distribution of SCC mec types among S. epidermidis is not known. SCC mec typing of a collection of 44 methicillin-resistant Staphylococcus epidermidis (MRSE) isolates recovered between 1973 and 1983 from the blood of patients with prosthetic valve endocarditis (PVE) was performed by PCR amplification of key genetic elements ( mecA , mecI , IS 1272 , and ccrAB ). Of the 44 isolates, 1 (2%) harbored SCC mec type I, 15 (34%) harbored type II, 12 (28%) harbored type III, and 16 (36%) harbored type IV. The complete nucleotide sequence of SCC mec type IV was determined for 16 isolates and found to be identical in size (24 kb) and 98% homologous to DNA sequences published for S. aureus . Type IV SCC mec was also common (5 of 10 isolates) among a geographically dispersed collection of 10 recent (1998 to 2001) S. epidermidis bloodstream isolates. Multilocus sequence typing (MLST) (using the same seven genes presently employed for S. aureus MLST) of these MRSE isolates and of 10 additional recent geographically dispersed methicillin-susceptible isolates demonstrated that all 16 PVE isolates and 2 of 5 recent isolates harboring type IV SCC mec were in three related clonal groups. All three MSSE PVE isolates recovered from patients between 1976 and 1979 were in the same clonal groups as type IV SCC mec MRSE isolates. These data support the hypothesis of intra- and interspecies transfer of type IV SCC mec and suggest that there are clonal associations in S. epidermidis that correlate with SCC mec type.