title: Evaluation of different microtiter plate-based methods for the quantitative assessment of Staphylococcus aureus biofilms.
abstract: OBJECTIVE
  To quantitatively assess Staphylococcus aureus biofilms.
  
  
  METHODS
  In addition to the qualitative Congo red agar (CRA) method, we used the bioluminescence (BLM), safranine (SAF), crystal violet (CRV) and resazurin (RES) high-throughput microtiter plate-based quantitative assays.
  
  
  RESULTS
  60.47% (26/43) of S. aureus clinical isolates were weak biofilm producers. The CRA method detected positive-slime phenotypes (13.95%), but was unable to distinguish weak from negative producers. BLM assays demonstrated significant correlations with RES (highest), CRV and SAF (lowest). Lower coefficient of variation values indicate precision. BLM scored highest precision (coefficient of variation = 0.013) followed by RES, SAF and CRV.
  
  
  CONCLUSIONS
  BLM and RES detect live biomass in S. aureus biofilms (for physiological studies). SAF and CRV detect live/dead bacteria plus biofilm matrix (for monitoring overall biofilm architecture, not only its cell viability). Reliable assays are essential for effective biofilm therapy.
authors.affiliation: Department of Microbiology & Immunology, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt.
authors.forename: Walid F
authors.initials: WF
authors.lastname: Elkhatib
authors.forename: Ahmed S
authors.initials: AS
authors.lastname: Khairalla
authors.forename: Hossam M
authors.initials: HM
authors.lastname: Ashour
mesh_terms: D018441:Biofilms / Q000254:growth & development*; D001681:Biological Assay / Q000379:methods*; D050296:Microbial Viability; D013211:Staphylococcus aureus / Q000254:growth & development*
keywords: Staphylococcus aureus; biofilm; bioluminescence; quantitation; safranine