title: Confocal laser scanning microscopy analysis of S. epidermidis biofilms exposed to farnesol, vancomycin and rifampicin.
abstract: BACKGROUND
  Staphylococcus epidermidis is the major bacterial species found in biofilm-related infections on indwelling medical devices. Microbial biofilms are communities of bacteria adhered to a surface and surrounded by an extracellular polymeric matrix. Biofilms have been associated with increased antibiotic tolerance to the immune system. This increased resistance to conventional antibiotic therapy has lead to the search for new antimicrobial therapeutical agents. Farnesol, a quorum-sensing molecule in Candida albicans, has been described as impairing growth of several different microorganisms and we have previously shown its potential as an adjuvant in antimicrobial therapy against S. epidermidis. However, its mechanism of action in S. epidermidis is not fully known. In this work we better elucidate the role of farnesol against S: epidermidis biofilms using confocal laser scanning microscopy (CLSM).
  
  
  RESULTS
  24 h biofilms were exposed to farnesol, vancomycin or rifampicin and were analysed by CLSM, after stained with a Live/Dead stain, a known indicator of cell viability, related with cell membrane integrity. Biofilms were also disrupted by sonication and viable and cultivable cells were quantified by colony forming units (CFU) plating. Farnesol showed a similar effect as vancomycin, both causing little reduction of cell viability but at the same time inducing significant changes in the biofilm structure. On the other hand, rifampicin showed a distinct action in S. epidermidis biofilms, by killing a significant proportion of biofilm bacteria.
  
  
  CONCLUSIONS
  While farnesol is not very efficient at killing biofilm bacteria, it damages cell membrane, as determined by the live/dead staining, in a similar way as vancomycin. Furthermore, farnesol might induce biofilm detachment, as determined by the reduced biofilm biomass, which can partially explain the previous findings regarding its role as a possible chemotherapy adjuvant.
authors.affiliation: Institute for Biotechnology and Bioengineering, Centre of Biological Engineering, University of Minho, Campus de Gualtar, Braga, Portugal. nunocerca@ceb.uminho.pt
authors.forename: Nuno
authors.initials: N
authors.lastname: Cerca
authors.forename: Fernanda
authors.initials: F
authors.lastname: Gomes
authors.forename: Sofia
authors.initials: S
authors.lastname: Pereira
authors.forename: Pilar
authors.initials: P
authors.lastname: Teixeira
authors.forename: Rosário
authors.initials: R
authors.lastname: Oliveira
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D018441:Biofilms / Q000187:drug effects* / Q000254:growth & development; D015169:Colony Count, Microbial; D005204:Farnesol / Q000494:pharmacology*; D005456:Fluorescent Dyes; D008826:Microbial Sensitivity Tests; D050296:Microbial Viability / Q000187:drug effects; D018613:Microscopy, Confocal; D012293:Rifampin / Q000494:pharmacology*; D013212:Staphylococcus epidermidis / Q000187:drug effects* / Q000254:growth & development / Q000648:ultrastructure; D014640:Vancomycin / Q000494:pharmacology*
chemical_list: D000900:Anti-Bacterial Agents; D005456:Fluorescent Dyes; D005204:Farnesol; D014640:Vancomycin; D012293:Rifampin