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

Abstract

We identified a new type of staphylococcal cassette chromosome mec (SCCmec) from two communityacquired 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-␤-lactam antibiotics, the type IV SCCmec was devoid of any antibiotic resistance genes other than the mecA gene.

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

“…Most CA-MRSA isolates harboring SCCmec type IV appear to be resistant to ␤-lactam antibiotics only and have a heterogeneous methicillin resistance phenotype that is consistent with the lack of any antibiotic genes other than mecA in this type of mec cassette (22,26,29). In our studies, most MRSA isolates hraboring SCCmec type IV were resistant to fewer antibiotics than were isolates harboring the other SCCmec types.…”

“…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). Isolate TAW166 had ccr type 2 and mec complex type B and was therefore classified as SCCmec type IV (22,29). However, as determined by the multiplex PCR strategy there was amplification of a locus specific for SCCmec type III that is located in the region between Tn554 and the chromosomal right junction (orfX) (28).…”

Type IV SCCmec found in decade old Brazilian MRSA isolates

“…The primers used for the classification of type IV SCCmec into IVa and IVb subtypes were most kindly provided by Dr. T. Ito [10]. For determining SCCmec subtype IVc, primers IVcF (5'-tctattcaatcgttctcgtattt-3') and IVcR (5'-tcgttgtcatttaattctgaact-3'), also provided by Dr. Ito, were used as described previously [10].…”

“…The CA-MRSA strains possess a SCCmec type designated type IV, which is physically smaller than the other SCCmec types and does not carry antimicrobial resistance genes other than the mecA gene [10]. They are usually more virulent than nosocomial MRSA, which, combined with their resistance to beta-lactams turns them into a menace, for infection can be fatal as has been previously reported [4].…”

Innate defences against methicillin‐resistant Staphylococcus aureus (MRSA) infection

“…The mec region is composed of mobile genetic elements that are called SCCmec cassettes. To date, five types of SCCmecs have been identified [35][36][37][38]. These cassettes have a variable size of about 20-70 kbp and contain mecA, , and other orf s of unknown function.…”