title: Bengal Bay clone ST772-MRSA-V outbreak: conserved clone causes investigation challenges.
abstract: BACKGROUND
  The Bengal Bay clone, ST772-MRSA-V, associated with multi-drug resistance, Panton-Valentine leukocidin (PVL) and skin and soft tissue infections, is emerging worldwide. In Norway, a country with low prevalence of meticillin-resistant Staphylococcus aureus (MRSA), increased occurrence of ST772-MRSA-V has also caused hospital outbreaks. The conserved nature of this clone challenged the outbreak investigations.
  
  
  OBJECTIVE
  To evaluate the usefulness of S. aureus protein A (spa) typing, multiple-locus variable number tandem repeat fingerprinting/analysis (MLVF/MLVA) and pulsed-field gel electrophoresis (PFGE) when investigating outbreaks with a conserved MRSA clone.
  
  
  METHODS
  A panel of 25 MRSA isolates collected in 2004-2014, consisting of six hospital outbreak isolates and 19 sporadic isolates, were analysed using spa typing, polymerase chain reaction detection of genes encoding PVL, MLVF/MLVA and PFGE.
  
  
  RESULTS
  All isolates were ST772-MRSA-V-t657 and resistant to erythromycin, gentamicin and norfloxacin, and 88% were PVL positive. PFGE could not discriminate between the isolates (≥85% similarity). MLVF resolved five types [Simpson's index of diversity (SID)=0.56], MLVA resolved six types (SID=0.66), and both methods separated the hospital isolates into two defined outbreaks.
  
  
  CONCLUSIONS
  MLVF/MLVA could not discriminate all epidemiologically unlinked cases and identical genotypes originated from a timespan of 10 years. MLVA was regarded as most suitable due to its higher discriminatory power and ability to provide unambiguous profiles. However, the Bengal Bay clone may require higher resolution methods for exact demarcation of outbreaks due to low diversity among isolates.
authors.affiliation: Department of Microbiology and Infection Control, Akershus University Hospital, Lørenskog, Norway. Electronic address: anita.blomfeldt@ahus.no.
authors.forename: A
authors.initials: A
authors.lastname: Blomfeldt
authors.affiliation: National Reference Laboratory for MRSA, Department of Medical Microbiology, St. Olavs University Hospital, Trondheim, Norway.
authors.forename: K W
authors.initials: KW
authors.lastname: Larssen
authors.affiliation: National Reference Laboratory for MRSA, Department of Medical Microbiology, St. Olavs University Hospital, Trondheim, Norway.
authors.forename: A
authors.initials: A
authors.lastname: Moghen
authors.affiliation: National Reference Laboratory for MRSA, Department of Medical Microbiology, St. Olavs University Hospital, Trondheim, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Haugum
authors.affiliation: Health Agency, City of Oslo, Norway.
authors.forename: T W
authors.initials: TW
authors.lastname: Steen
authors.affiliation: Department of Microbiology and Infection Control, Akershus University Hospital, Lørenskog, Norway.
authors.forename: S B
authors.initials: SB
authors.lastname: Jørgensen
authors.affiliation: Department of Microbiology and Infection Control, Akershus University Hospital, Lørenskog, Norway; Department of Clinical Molecular Biology (EpiGen), Akershus University Hospital and University of Oslo, Lørenskog, Norway.
authors.forename: H V
authors.initials: HV
authors.lastname: Aamot
mesh_terms: D002999:Clone Cells; D003428:Cross Infection / Q000453:epidemiology* / Q000382:microbiology; D004196:Disease Outbreaks; D005838:Genotype; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000145:classification* / Q000235:genetics / Q000302:isolation & purification*; D017720:Molecular Epidemiology / Q000379:methods; D058889:Molecular Typing / Q000379:methods*; D009664:Norway / Q000453:epidemiology; D013203:Staphylococcal Infections / Q000453:epidemiology* / Q000382:microbiology
keywords: MLVF/MLVA; Outbreak; PFGE; ST772-MRSA-V; Staphylococcus aureus; spa typing