title: Comparative genomics of vancomycin-resistant Staphylococcus aureus strains and their positions within the clade most commonly associated with Methicillin-resistant S. aureus hospital-acquired infection in the United States.
abstract: Methicillin-resistant Staphylococcus aureus (MRSA) strains are leading causes of hospital-acquired infections in the United States, and clonal cluster 5 (CC5) is the predominant lineage responsible for these infections. Since 2002, there have been 12 cases of vancomycin-resistant S. aureus (VRSA) infection in the United States-all CC5 strains. To understand this genetic background and what distinguishes it from other lineages, we generated and analyzed high-quality draft genome sequences for all available VRSA strains. Sequence comparisons show unambiguously that each strain independently acquired Tn1546 and that all VRSA strains last shared a common ancestor over 50 years ago, well before the occurrence of vancomycin resistance in this species. In contrast to existing hypotheses on what predisposes this lineage to acquire Tn1546, the barrier posed by restriction systems appears to be intact in most VRSA strains. However, VRSA (and other CC5) strains were found to possess a constellation of traits that appears to be optimized for proliferation in precisely the types of polymicrobic infection where transfer could occur. They lack a bacteriocin operon that would be predicted to limit the occurrence of non-CC5 strains in mixed infection and harbor a cluster of unique superantigens and lipoproteins to confound host immunity. A frameshift in dprA, which in other microbes influences uptake of foreign DNA, may also make this lineage conducive to foreign DNA acquisition.
  
  
  OBJECTIVE
  Invasive methicillin-resistant Staphylococcus aureus (MRSA) infection now ranks among the leading causes of death in the United States. Vancomycin is a key last-line bactericidal drug for treating these infections. However, since 2002, vancomycin resistance has entered this species. Of the now 12 cases of vancomycin-resistant S. aureus (VRSA), each was believed to represent a new acquisition of the vancomycin-resistant transposon Tn1546 from enterococcal donors. All acquisitions of Tn1546 so far have occurred in MRSA strains of the clonal cluster 5 genetic background, the most common hospital lineage causing hospital-acquired MRSA infection. To understand the nature of these strains, we determined and examined the nucleotide sequences of the genomes of all available VRSA. Genome comparison identified candidate features that position strains of this lineage well for acquiring resistance to antibiotics in mixed infection.
authors.affiliation: Department of Ophthalmology, Harvard Microbial Sciences Initiative, Harvard Medical School, Massachusetts Eye and Ear Infirmary, Boston, Massachusetts, USA.
authors.forename: Veronica N
authors.initials: VN
authors.lastname: Kos
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Desjardins
authors.forename: Allison
authors.initials: A
authors.lastname: Griggs
authors.forename: Gustavo
authors.initials: G
authors.lastname: Cerqueira
authors.forename: Andries
authors.initials: A
authors.lastname: Van Tonder
authors.forename: Matthew T G
authors.initials: MT
authors.lastname: Holden
authors.forename: Paul
authors.initials: P
authors.lastname: Godfrey
authors.forename: Kelli L
authors.initials: KL
authors.lastname: Palmer
authors.forename: Kip
authors.initials: K
authors.lastname: Bodi
authors.forename: Emmanuel F
authors.initials: EF
authors.lastname: Mongodin
authors.forename: Jennifer
authors.initials: J
authors.lastname: Wortman
authors.forename: Michael
authors.initials: M
authors.lastname: Feldgarden
authors.forename: Trevor
authors.initials: T
authors.lastname: Lawley
authors.forename: Steven R
authors.initials: SR
authors.lastname: Gill
authors.forename: Brian J
authors.initials: BJ
authors.lastname: Haas
authors.forename: Bruce
authors.initials: B
authors.lastname: Birren
authors.forename: Michael S
authors.initials: MS
authors.lastname: Gilmore
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology*; D023281:Genomics; D006801:Humans; D016106:Methicillin Resistance; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification* / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D008969:Molecular Sequence Data; D010802:Phylogeny; D016415:Sequence Alignment; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000145:classification* / Q000187:drug effects / Q000235:genetics* / Q000302:isolation & purification; D014481:United States / Q000453:epidemiology; D020713:Vancomycin Resistance
chemical_list: D001426:Bacterial Proteins