Seven novel variants of the staphylococcal chromosomal cassette mec in methicillin-resistant Staphylococcus aureus isolates from Ireland

Methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered in Irish hospitals between 1971 and 2002 were characterized using multilocus sequence typing (MLST) (n = 130) and SCCmec typing (n = 172). Where atypical SCCmec typing results were obtained, PCR amplification of entire SCCmec elements, analysis of amplimer mobility, and nucleotide sequencing were undertaken. MLST revealed that 129/130 isolates had the same genotypes as internationally spread MRSA clones, including ST239, ST247, ST250, ST5, ST22, ST36, and ST8. A novel genotype, ST496, was identified in one isolate. Half of the isolates (86/172) had SCCmec type I, IA, II, III, or IV. The remaining 86 isolates harbored novel SCCmec variants in three distinct genetic backgrounds: (i) 74/86 had genotype ST8 and either one of five novel SCCmec II (IIA, IIB, IIC, IID, and IIE) or one of two novel SCCmec IV (IVE and IVF) variants; (ii) 3/86 had genotype ST239 and a novel SCCmec III variant; (iii) 9/86 had a novel SCCmec I variant associated with ST250. SCCmec IVE and IVF were similar to SCCmec IVc and IVb, respectively, but differed in the region downstream of mecA. The five SCCmec II variants were similar to SCCmec IVb in the region upstream of the ccr complex but otherwise were similar to SCCmec II, except for the following regions: SCCmec IIA and IID had a novel mec complex, A.4 (Delta mecI-IS1182-Delta mecI-mecRI-mecA-IS431mec); SCCmec TIC and TIE had a novel mec complex, A.3 (IS1182-Delta mecI-mecR1-mecA-IS431mec); SCCmec IID and TIE lacked pUB110; SCCmec TIC and TIE lacked a region of DNA between Tn554 and the mec complex; and SCCmec 1113 lacked Tn554. This study has demonstrated a hitherto-undescribed degree of diversity within SCCmec.