title: Characterization of a novel arginine catabolic mobile element (ACME) and staphylococcal chromosomal cassette mec composite island with significant homology to Staphylococcus epidermidis ACME type II in methicillin-resistant Staphylococcus aureus genotype ST22-MRSA-IV.
abstract: The arginine catabolic mobile element (ACME) is prevalent among methicillin-resistant Staphylococcus aureus (MRSA) isolates of sequence type 8 (ST8) and staphylococcal chromosomal cassette mec (SCCmec) type IVa (USA300) (ST8-MRSA-IVa isolates), and evidence suggests that ACME enhances the ability of ST8-MRSA-IVa to grow and survive on its host. ACME has been identified in a small number of isolates belonging to other MRSA clones but is widespread among coagulase-negative staphylococci (CoNS). This study reports the first description of ACME in two distinct strains of the pandemic ST22-MRSA-IV clone. A total of 238 MRSA isolates recovered in Ireland between 1971 and 2008 were investigated for ACME using a DNA microarray. Twenty-three isolates (9.7%) were ACME positive, and all were either MRSA genotype ST8-MRSA-IVa (7/23, 30%) or MRSA genotype ST22-MRSA-IV (16/23, 70%). Whole-genome sequencing and comprehensive molecular characterization revealed the presence of a novel 46-kb ACME and staphylococcal chromosomal cassette mec (SCCmec) composite island (ACME/SCCmec-CI) in ST22-MRSA-IVh isolates (n=15). This ACME/SCCmec-CI consists of a 12-kb DNA region previously identified in ACME type II in S. epidermidis ATCC 12228, a truncated copy of the J1 region of SCCmec type I, and a complete SCCmec type IVh element. The composite island has a novel genetic organization, with ACME located within orfX and SCCmec located downstream of ACME. One PVL locus-positive ST22-MRSA-IVa isolate carried ACME located downstream of SCCmec type IVa, as previously described in ST8-MRSA-IVa. These results suggest that ACME has been acquired by ST22-MRSA-IV on two independent occasions. At least one of these instances may have involved horizontal transfer and recombination events between MRSA and CoNS. The presence of ACME may enhance dissemination of ST22-MRSA-IV, an already successful MRSA clone.
authors.affiliation: Microbiology Research Unit, Division of Oral Biosciences, Dublin Dental University Hospital, University of Dublin, Trinity College Dublin, Lincoln Place, Dublin 2, Ireland.
authors.forename: Anna C
authors.initials: AC
authors.lastname: Shore
authors.forename: Angela S
authors.initials: AS
authors.lastname: Rossney
authors.forename: Orla M
authors.initials: OM
authors.lastname: Brennan
authors.forename: Peter M
authors.initials: PM
authors.lastname: Kinnevey
authors.forename: Hilary
authors.initials: H
authors.lastname: Humphreys
authors.forename: Derek J
authors.initials: DJ
authors.lastname: Sullivan
authors.forename: Richard V
authors.initials: RV
authors.lastname: Goering
authors.forename: Ralf
authors.initials: R
authors.lastname: Ehricht
authors.forename: Stefan
authors.initials: S
authors.lastname: Monecke
authors.forename: David C
authors.initials: DC
authors.lastname: Coleman
mesh_terms: D005838:Genotype; D055624:Methicillin-Resistant Staphylococcus aureus / Q000235:genetics*; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D016133:Polymerase Chain Reaction; D013212:Staphylococcus epidermidis / Q000235:genetics*