Novel Type of Staphylococcal Cassette Chromosome mec Identified in Community-Acquired Methicillin-Resistant Staphylococcus aureus Strains

We identified a new type of staphylococcal cassette chromosome mec (SCCmec) from two community-acquired methicillin-resistant Staphylococcus aureus (MRSA) strains. The novel element, designated type IV SCCmec, had a unique combination of the class B mec gene complex and the type 2 ccr gene complex and was much smaller in size (21 to 24 kb) than previously identified SCCmec elements of hospital-acquired MRSA. Consistent with the strains' susceptibilities to various non-β-lactam antibiotics, the type IV SCCmec was devoid of any antibiotic resistance genes other than the mecA gene

Staphylococcal Cassette Chromosome mec (SCCmec) Typing of Methicillin-Resistant Staphylococcus aureus Strains Isolated in 11 Asian Countries: a Proposal for a New Nomenclature for SCCmec Elements

A description of staphylococcal cassette chromosome mec (SCCmec) elements carried by 615 methicillin-resistant Staphylococcus aureus (MRSA) strains isolated in 11 Asian countries is reported, and a novel nomenclatural system based on their structures is proposed. The 615 strains were classified as type 3A (370 strains), type 2A (207 strains), type 2B (32 strains), type 1B (1 strain), and nontypeable (5 strains). The previously reported type III SCCmec (DDBJ/EMBL/GenBank accession no. AB037671) carried by the MRSA strain 85/2082 was ascertained to be composed of two SCC elements, type 3A SCCmec and SCCmercury. PCR analysis indicated that 310 of 370 type 3A SCCmec strains carried both SCC elements. These strains were prevalent in eight countries: Thailand, Sri Lanka, Indonesia, Vietnam, Philippines, Saudi Arabia, India, and Singapore. The remaining 60 type 3A SCCmec strains differed with respect to the left extremity polymorphism or to the presence of ccrC. Among these, two were identified as carrying only type 3A SCCmec elements, but their left extremities differed. Type 2A SCCmec strains predominated in Korea and Japan, although the frequency of the presence of ant(4′)-1 gene downstream of mecA varied (53% for Korean strains; 93% for Japanese strains). Various SCCmec elements were identified in the tested strains, and limited numbers were identified by their multilocus sequence typing genotypes. These data suggest that numerous MRSA clones are disseminated in Asian hospitals, and these consist of minor clones that are presumed to have arisen locally and major clones that are presumed to have been introduced from other countries

Dissemination of New Methicillin-Resistant Staphylococcus aureus Clones in the Community

Multiple methicillin-resistant Staphylococcus aureus (MRSA) clones carrying type IV staphylococcal cassette chromosome mec were identified in the community-acquired MRSA strains of both the United States and Australia. They multiplied much faster than health-care-associated MRSA and were resistant to fewer non-beta-lactam antibiotics. They seem to have been derived from more diverse S. aureus populations than health-care-associated MRSA strains