title: Rifampicin fails to eradicate mature biofilm formed by methicillin-resistant Staphylococcus aureus.
abstract: BACKGROUND
  Antimicrobial activity on biofilms depends on their molecular size, positive charges, permeability coefficient, and bactericidal activity. Vancomycin is the primary choice for methicillin-resistant Staphylococcus aureus (MRSA) infection treatment; rifampicin has interesting antibiofilm properties, but its effectivity remains poorly defined.
  
  
  METHODS
  Rifampicin activity alone and in combination with vancomycin against biofilm-forming MRSA was investigated, using a twofold serial broth microtiter method, biofilm challenge, and bacterial count recovery.
  
  
  RESULTS
  Minimal inhibitory concentration (MIC) and minimal bactericidal concentration for vancomycin and rifampicin ranged from 0.5 to 1mg/l and 0.008 to 4mg/l, and from 1 to 4mg/l and 0.06 to 32mg/l, respectively. Mature biofilms were submitted to rifampicin and vancomycin exposure, and minimum biofilm eradication concentration ranged from 64 to 32,000 folds and from 32 to 512 folds higher than those for planktonic cells, respectively. Vancomycin (15mg/l) in combination with rifampicin at 6 dilutions higher each isolate MIC did not reach in vitro biofilm eradication but showed biofilm inhibitory capacity (1.43 and 0.56log10 CFU/ml reduction for weak and strong biofilm producers, respectively; p<0.05).
  
  
  CONCLUSIONS
  In our setting, rifampicin alone failed to effectively kill biofilm-forming MRSA, demonstrating stronger inability to eradicate mature biofilm compared with vancomycin.
authors.affiliation: Programa de Pós-graduação em Ciências da Saúde, Universidade Federal de Ciências da Saúde de Porto Alegre, Porto Alegre, RS, Brasil. kelicrisr@gmail.com
authors.forename: Keli Cristine
authors.initials: KC
authors.lastname: Reiter
authors.forename: Gustavo Enck
authors.initials: GE
authors.lastname: Sambrano
authors.forename: Bárbara
authors.initials: B
authors.lastname: Villa
authors.forename: Thiago Galvão da Silva
authors.initials: TG
authors.lastname: Paim
authors.forename: Caio Fernando
authors.initials: CF
authors.lastname: de Oliveira
authors.forename: Pedro Alves
authors.initials: PA
authors.lastname: d'Azevedo
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D006801:Humans; D055624:Methicillin-Resistant Staphylococcus aureus / Q000502:physiology*; D008826:Microbial Sensitivity Tests; D012293:Rifampin / Q000494:pharmacology*; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D014640:Vancomycin; D012293:Rifampin