Biofilm : mise en place et organisation d’une communauté bactérienne Biofilm : positioning and organisation of bacterial communities

Résumé

Durant ces 20 dernières années, les microbiologistes ont pris conscience que le mode de croissance bactérien utilisé en laboratoire avait ses limites. En effet, dans leur environnement naturel, les micro-organismes sont attachés à une surface, organisés en communautés structurées, et englobés dans une matrice d’exopolysaccharide. Ce mode de développement, appelé biofilm, a pris une importance toute particulière lorsqu’il a été établi qu’il était impliqué dans un grand nombre d’infections bactériennes. Pseudomonas aeruginosa est un pathogène opportuniste responsable d’infections nosocomiales et d’infections irréversibles et mortelles chez les malades souffrant de mucoviscidose. Cet organisme s’installe dans les tissus sous forme de biofilm, mais est également capable d’adhérer à des surfaces inertes. Le développement de cribles génétiques et le séquençage du génome de P. aeruginosa ont permis d’obtenir de nombreuses informations permettant de mieux comprendre ce phénomène au niveau moléculaire.

Summary

Bacterial attachment on various surfaces mostly takes place in the form of specialised bacterial communities, referred to as biofilm. The biofilm is formed through series of interactions between cells and adherence to surface, resulting in an organised structure. In this review we have been using Pseudomonas aeruginosa as a model microorganism to describe the series of events that occurred during this developmental process. P. aeruginosa is an opportunistic pathogen that has a wide variety of hosts and infectious sites. In addition to biofilm formation in certain tissues, inert surfaces, such as catheters, are also target for bacterial biofilm development. The use of convenient genetic screens has made possible the identification of numerous biofilm-defective mutants, which have been characterised further. These studies have allowed the proposal for a global model, in which key events are described for the different stages of biofilm formation. Briefly, flagellar mobility is crucial for approaching the surface, whereas type IV pili motility is preponderant for surface colonisation and microcolonies formation. These microcolonies are finally packed together and buried in an exopolysaccharide matrix to form the differentiated biofilm. It is obvious that the different stages of biofilm formation also involved perception of environmental stimuli. These stimuli, and their associated complex regulatory networks, have still to be fully characterised to understand the bacterial strategy, which initiates biofilm formation. One such regulatory system, called Quorum sensing, is one of the key player in the initial differentiation of biofilm. Finally, a better understanding, at the molecular level, of biofilm establishment and persistence should help for the design of antimicrobials that prevent bacterial infections.