Seven Novel Variants of the Staphylococcal Chromosomal Cassette mec in Methicillin-Resistant Staphylococcus aureus Isolates from Ireland

Abstract

Methicillin-resistant Staphylococcus aureus (MRSA) isolates recovered in Irish hospitals between 1971 and 2002 were characterized using multilocus sequence typing (MLST) ( n = 130) and SCC mec typing ( n = 172). Where atypical SCC mec typing results were obtained, PCR amplification of entire SCC mec 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 SCC mec type I, IA, II, III, or IV. The remaining 86 isolates harbored novel SCC mec variants in three distinct genetic backgrounds: (i) 74/86 had genotype ST8 and either one of five novel SCC mec II (IIA, IIB, IIC, IID, and IIE) or one of two novel SCC mec IV (IVE and IVF) variants; (ii) 3/86 had genotype ST239 and a novel SCC mec III variant; (iii) 9/86 had a novel SCC mec I variant associated with ST250. SCC mec IVE and IVF were similar to SCC mec IVc and IVb, respectively, but differed in the region downstream of mecA . The five SCC mec II variants were similar to SCC mec IVb in the region upstream of the ccr complex but otherwise were similar to SCC mec II, except for the following regions: SCC mec IIA and IID had a novel mec complex, A.4 (Δ mecI -IS 1182- Δ mecI-mecR1-mecA- IS 431mec ); SCC mec IIC and IIE had a novel mec complex, A.3 (IS 1182 -Δ mecI - mecR1-mecA- IS 431mec ); SCC mec IID and IIE lacked pUB110; SCC mec IIC and IIE lacked a region of DNA between Tn 554 and the mec complex; and SCC mec IIB lacked Tn 554 . This study has demonstrated a hitherto-undescribed degree of diversity within SCC mec .