Pseudomonas aeruginosa: A model for biofilm formation

Abstract

Much of the fundamental understanding of microbial physiology is based on laboratory studies of freely suspended cells. While these studies have been essential for our foundational understanding of the genetics, physiology and behavior of microbes, it is now recognized that a majority of bacterial cells in nature exist in biofilms [1] associated with surfaces or as floating cell aggregates. In fact, it has recently been proposed that microbial communities originally developed on surfaces, including the first bacterial and archael cells, and that the planktonic cell phenotype evolved as a dispersal mechanism [2]. Hallmarks of cells residing in biofilm communities are increased metabolic efficiency [3] as well as increased resistance to environmental stresses such as desiccation, ultraviolet radiation and oxidative stress [4–6]. This correlation has dramatic consequences as residing in aggregates has been shown to confer increased resistance of bacterial cells also to biocides such as antibiotics, disinfectants and detergents [7–9]. In addition, once established, these biofilms are able to resist invasion by other organisms and predation by protozoans in nature or host immune cells in the human body [5,6,10]. This is especially problematic as 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 an enhanced appreciation for the multicellular aspects of microbiology and has resulted in the general acceptance of a model of the biofilm mode of life. Pseudomonas aeruginosa has become a model organism for the study of biofilms due to its metabolic versatility and variability in its response to environmental signals, which promotes successful colonization of different habitats and growth under varying environmental conditions [12,13]. This ability is likely a reflection of its large genome, allowing for metabolic plasticity and quick responses to varying stimuli. P. aeruginosa is also a human pathogen that causes infection in burn patients, and is the 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.