title: Investigation of Biofilm Formation and its Association with the Molecular and Clinical Characteristics of Methicillin-resistant Staphylococcus aureus.
abstract: OBJECTIVE
  To investigate the biofilm-forming related factors against MRSA bloodstream isolates and evaluates their clinical features and treatment outcomes by biofilm production.
  
  
  METHODS
  We collected 126 consecutive methicillin-resistant Staphylococcus aureus (MRSA) causing blood stream infections (BSIs) at 10 tertiary hospitals from 2007 to 2009. We investigated biofilm-forming ability using a microtiter plate assay, and molecular characteristics including multilocus sequence typing, staphylococcal cassette chromosome mec and accessory gene regulator types. We compared the clinical characteristics and outcomes of patients infected with biofilm-forming and non-biofilm-forming MRSA isolates.
  
  
  RESULTS
  Of the 126 samples, 86 (68.3%), including 5 strong level (OD570 ≥ 1.0) and 81 weak level (0.2 ≤ OD570 < 1.0), had biofilm-forming capacity. Detection of fibronectinbinding protein in biofilm-forming strains was significantly higher than biofilm non-forming ones (p = 0.001) and three enterotoxin genes (sec-seg-sei) islands had a high frequency regardless of biofilm production. However, biofilm-forming strains were more likely to be multidrug resistant (three or more non-β-lactam antibiotics) than biofilm non-forming ones [79.2% vs. 59.2%, p = 0.015, odds ratio (OR) 2.629, 95% confidence interval (CI) 1.92-5.81]. Clinical features of patients with BSIs caused by biofilm-forming MRSA strains were more likely to be hospital onset [77.9% vs. 60.0%, p = 0.024, OR 2.434, 95% CI 1.11-5.33) and more frequently occurred in patients with use of invasive devices [85.7% vs. 61.2%, p = 0.002, OR 3.879, 95% CI 1.61-8.97]. The other clinical features were compared with the clinical outcomes of the two groups and were not significant (p > 0.05).
  
  
  CONCLUSIONS
  Biofilm-forming MRSA strains showed higher frequency of fnbB gene than biofilm non-forming ones and more incidence rates on particular genotypes. And, their patient's features were not significantly different between two groups in this study, except for several clinical factors.
authors.affiliation: Division of Antimicrobial Resistance, Korea National Institute of Health, Osong, Korea.
authors.forename: Jeong-Ok
authors.initials: JO
authors.lastname: Cha
authors.forename: Jae Il
authors.initials: JI
authors.lastname: Yoo
authors.forename: Jung Sik
authors.initials: JS
authors.lastname: Yoo
authors.forename: Hae-Sun
authors.initials: HS
authors.lastname: Chung
authors.forename: Sun-Hee
authors.initials: SH
authors.lastname: Park
authors.forename: Hwa Su
authors.initials: HS
authors.lastname: Kim
authors.forename: Yeong Seon
authors.initials: YS
authors.lastname: Lee
authors.forename: Gyung Tae
authors.initials: GT
authors.lastname: Chung
keywords: biofilm; blood stream infection; clinical features; methicillin-resistant Staphylococcus aureus