title: Variability in SCCmecN1 spreading among injection drug users in Zurich, Switzerland.
abstract: BACKGROUND
  An extremely low level methicillin resistant Staphylococcus aureus (MRSA) belonging to ST45, circulates among intravenous drug users in the Zurich area. This clone can be misinterpreted as an MSSA by phenotypic oxacillin resistance tests, although it carries a staphylococcal cassette chromosome mec (SCCmec) element encoding a functional mecA gene and it produces PBP2a.
  
  
  RESULTS
  This clone carried a new 45.7-kb element, termed SCCmecN1, containing a class B mec complex (mecA-DeltamecR1::IS1272), a truncated Tn4003 harbouring the dfrA gene, and a fusB1 gene, conferring methicillin, trimethoprim and low level fusidic acid resistance, respectively. In addition to the two insertion site sequences (ISS) framing the SCCmec, a third ISS (ISS*) was identified within the element. SCCmecN1 also harboured two distinct ccrAB complexes belonging to the class 4 subtype, both of which were shown to be active and to be able to excise the SCCmecN1 or parts thereof. Slight variations in the SmaI-PFGE pattern of the clinical MRSA isolates belonging to this clone were traced back to differences in the sizes of the SCCmec J2 regions and/or to a 6.4-kb deletion extending from ISS* to the right end ISS. This latter deletion led to a variant right SCCmec-chromosomal junction site. MRSA clones carrying the shorter SCCmec with the 6.4-kb deletion were usually ciprofloxacin resistant, while strains with the complete SCCmecN1 were co-trimoxazole resistant or had no additional resistances. This suggested that the genetic backbone of the host S. aureus, although identical by PFGE pattern, had at some stage diverged with one branch acquiring a sulfonomide resistance mutation and the other ciprofloxacin resistance.
  
  
  CONCLUSIONS
  This description of the structure and variations of SCCmecN1 will allow for quicker and easier molecular detection of this clone and monitoring of its spread.
authors.affiliation: Institute of Medical Microbiology, University of Zurich, Zurich, Switzerland. mender@immv.uzh.ch <mender@immv.uzh.ch>
authors.forename: Miriam
authors.initials: M
authors.lastname: Ender
authors.forename: Brigitte
authors.initials: B
authors.lastname: Berger-Bächi
authors.forename: Nadine
authors.initials: N
authors.lastname: McCallum
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001426:Bacterial Proteins / Q000235:genetics; D002939:Ciprofloxacin / Q000494:pharmacology; D016172:DNA Fingerprinting; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry / Q000235:genetics; D015252:Deoxyribonucleases, Type II Site-Specific / Q000378:metabolism; D005672:Fusidic Acid / Q000494:pharmacology; D006801:Humans; D020071:Interspersed Repetitive Sequences; D008712:Methicillin / Q000494:pharmacology; D016106:Methicillin Resistance / Q000235:genetics*; D017720:Molecular Epidemiology; D008969:Molecular Sequence Data; D046915:Penicillin-Binding Proteins; D012150:Polymorphism, Restriction Fragment Length; D013203:Staphylococcal Infections / Q000453:epidemiology / Q000382:microbiology*; D013211:Staphylococcus aureus / Q000187:drug effects / Q000235:genetics*; D015819:Substance Abuse, Intravenous / Q000382:microbiology*; D013557:Switzerland; D014295:Trimethoprim / Q000494:pharmacology; D015662:Trimethoprim, Sulfamethoxazole Drug Combination / Q000494:pharmacology
chemical_list: D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D004251:DNA Transposable Elements; D004269:DNA, Bacterial; C492443:FusB protein, Staphylococcus aureus; D046915:Penicillin-Binding Proteins; C487789:mecA protein, Staphylococcus aureus; D005672:Fusidic Acid; D002939:Ciprofloxacin; D015662:Trimethoprim, Sulfamethoxazole Drug Combination; D014295:Trimethoprim; C025651:CCCGGG-specific type II deoxyribonucleases; D015252:Deoxyribonucleases, Type II Site-Specific; D008712:Methicillin