Is biofilm a cause of silent chronic inflammation in haemodialysis patients? A fascinating working hypothesis

Abstract

Knowledge of biofilm formation and its biological rolein chronic subclinical inflammation has largely evolvedover the past years [1–5]. The development of a biofilmis a very effective way for bacteria to survive facinghostile conditions and to resist biocides and antimicro-bial substances. The initial event in biofilm formationis the adhesion of microbes to surfaces. The surfaceproperties of medical devices are usually modified bya conditioning film of organic material. The effect ofsingle blood proteins or of whole blood itself dependson bacterial strains. Fibrinogen and fibronectin bothenhance Staphylococcus aureus binding and inhibitStaphylococcus epidermidis or Gram-negative bacteriaadherence, while whole blood promotes Pseudomonasaeruginosa biofilm formation [6].Biofilm is not a static simple matrix made ofhomogeneous slime embedding bacteria. This sessilemulticellular community is a dynamic complex systemmade of exopolysaccharide matrix embedding livingmicroorganisms with a phenotype modified fromplanktonic (free-floating) bacteria. Biofilm is a livingmaterial that evolves according to local microenviron-mental conditions (hydrodynamic and biochemicalconditions, thickness, shear stress and possiblyothers). Biofilm has a spatial heterogeneity (channels,towers) that seems to be linked to the type of bacteriaand may differ in relation to oxygen limitation, pH,nutrient access and growth rates.However, despite these important acquisitions, therole of biofilm in haemodialysis patients is undefined.At present, we are unable to define the extent and theincidence of biofilm formation in the haemodialysispopulation. No method exists to detect biofilm in vivoand to ascertain its eradication. In principle, bacteriaare often shown to form biofilm using ‘extreme’ andunrealistic experimental conditions. Detection of bio-film is usually performed by surface ultrastructuralanalysis alone or in combination with methods tostain the bacterial nuclear DNA using membrane-permeable or impermeable fluorochromes (to detectdead or live bacteria, respectively). In this editorial,we will describe several potential sites of bacterialcontamination and possibly of biofilm formation inhaemodialyis patients, such as the vascular access(arterio-venous fistula and graft or venous catheters)and the hydraulic circuit of the water treatment andof haemodialysis monitors.