Pseudomonas aeruginosa: A model for biofilm formation

Much of the fundamental understanding of microbial physiology is based onlaboratory studies of freely suspended cells. While these studies have been essentialfor our foundational understanding of the genetics, physiology and behavior ofmicrobes, it is now recognized that a majority of bacterial cells in nature exist inbiofilms [1] associated with surfaces or as floating cell aggregates. In fact, it hasrecently been proposed that microbial communities originally developed on surfaces,including the first bacterial and archael cells, and that the planktonic cell phenotypeevolved as a dispersal mechanism [2]. Hallmarks of cells residing in biofilmcommunities are increased metabolic efficiency [3] as well as increased resistanceto environmental stresses such as desiccation, ultraviolet radiation and oxidativestress [4–6]. This correlation has dramatic consequences as residing in aggregateshas been shown to confer increased resistance of bacterial cells also to biocides suchas antibiotics, disinfectants and detergents [7–9]. In addition, once established, thesebiofilms are able to resist invasion by other organisms and predation by protozoans innature or host immune cells in the human body [5,6,10]. This is especially problematicas it is also recognized that the majority of bacterial infections involve biofilms[11]. The recent explosion of research in the field of biofilm biology has led to anenhanced appreciation for the multicellular aspects of microbiology and has resultedin the general acceptance of a model of the biofilm mode of life.Pseudomonas aeruginosa has become a model organism for the study of biofilmsdue to its metabolic versatility and variability in its response to environmental signals,which promotes successful colonization of different habitats and growth undervarying environmental conditions [12,13]. This ability is likely a reflection of its largegenome, allowing for metabolic plasticity and quick responses to varying stimuli.P. aeruginosa is also a human pathogen that causes infection in burn patients, and isthe predominant cause of lung infections and mortality in patients with cystic fibrosis (CF) [14,15]. This chapter will address various aspects of biofilm development,dispersal and resistance, and its role in the infection process