Antimicrob Agents Chemother 2001 May;45(5):1323-36
Department of Bacteriology, Juntendo University, Tokyo 113-8421, Japan.
The beta-lactam resistance gene mecA of Staphylococcus aureus is carried by
a novel mobile genetic element, designated staphylococcal cassette
chromosome mec (SCCmec), identified in the chromosome of a Japanese
methicillin-resistant S. aureus (MRSA) strain. We now report identification
of two additional types of mecA-carrying genetic elements found in the MRSA
strains isolated in other countries of the world. There were substantial
differences in the size and nucleotide sequences between the elements and
the SCCmec. However, new elements shared the chromosomal integration site
with the SCCmec. Structural analysis of the new elements revealed that they
possessed all of the salient features of the SCCmec: conserved terminal
inverted repeats and direct repeats at the integration junction points,
conserved genetic organization around the mecA gene, and the presence of
cassette chromosome recombinase (ccr) genes responsible for the movements
of SCCmec. The elements, therefore, were considered to comprise the SCCmec
family of staphylococcal mobile genetic elements together with the
previously identified SCCmec. Among 38 epidemic MRSA strains isolated in 20
countries, 34 were shown to possess one of the three typical SCCmec
elements on the chromosome. Our findings indicated that there are at least
three distinct MRSA clones in the world with different types of SCCmec in
their chromosome.