Structural Comparison of Three Types of Staphylococcal Cassette Chromosome mec Integrated in the Chromosome in Methicillin-Resistant Staphylococcus aureus

Abstract

The ␤-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 mecAcarrying 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.

Evolution of Sporadic Isolates of Methicillin-Resistant Staphylococcus aureus (MRSA) in Hospitals and Their Similarities to Isolates of Community-Acquired MRSA

“…Isolate HSA10 had ccr type 3 and mec complex type A and was therefore classified as SCCmec type III (19). However, by the multiplex PCR strategy it was determined that there was amplification of the locus corresponding to the dcs region that was not detectable in the SCCmec type III of previously characterized MRSA strains (19,28,29). Isolates JP87 and JP238 had ccr type 2 and mec complex type A and were therefore classified as SCCmec type II (19).…”

“…For these four isolates, SCCmec types were determined by PCR typing the mec gene and the ccr gene complexes (26). Isolate HSA10 had ccr type 3 and mec complex type A and was therefore classified as SCCmec type III (19). However, by the multiplex PCR strategy it was determined that there was amplification of the locus corresponding to the dcs region that was not detectable in the SCCmec type III of previously characterized MRSA strains (19,28,29).…”

“…However, by the multiplex PCR strategy it was determined that there was amplification of the locus corresponding to the dcs region that was not detectable in the SCCmec type III of previously characterized MRSA strains (19,28,29). Isolates JP87 and JP238 had ccr type 2 and mec complex type A and were therefore classified as SCCmec type II (19). However, by the multiplex PCR strategy there was no amplification of the locus corresponding to the kdp operon (29) or the locus corresponding to the mecI gene, in spite of the fact that both of these genes were present in previously characterized SCCmec type II (19,29).…”

Emergence of SCCmec Type IV as the Most Common Type of Methicillin-Resistant Staphylococcus aureus in a University Hospital

“…SCCmec is a mobile DNA element of 21-67 kb and is integrated into the chromosome of MRSA [1,2]. Hospital-associated MRSA (HA-MRSA) isolates are typically resistant to multiple antibiotics, negative for Panton-Valentine leukocidin (PVL) encoding genes and primarily harbor SCCmec types I, II, III, and rarely IV [1,3,4].…”

“…Hospital-associated MRSA (HA-MRSA) isolates are typically resistant to multiple antibiotics, negative for Panton-Valentine leukocidin (PVL) encoding genes and primarily harbor SCCmec types I, II, III, and rarely IV [1,3,4]. Up to six main types of SCCmec and many variants, especially of type IV are known [1,5,6]. Type IV is present in many more genetic backgrounds than other types suggesting an enhanced mobility [7][8][9].…”