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1 - Quorum sensing and regulation of Pseudomonas aeruginosa infections
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- By Victoria E. Wagner, University of Rochester School of Medicine and Dentistry Rochester, NY USA, Barbara H. Iglewski, University of Rochester School of Medicine and Dentistry Rochester, NY USA
- Edited by Donald R. Demuth, University of Louisville, Kentucky, Richard Lamont, University of Florida
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- Book:
- Bacterial Cell-to-Cell Communication
- Published online:
- 08 August 2009
- Print publication:
- 23 February 2006, pp 1-22
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Summary
INTRODUCTION
Pseudomonas aeruginosa is a ubiquitous Gram-negative microorganism that thrives in many environments, from soil and water to animals and people. It is an opportunistic pathogen that can cause respiratory infections, urinary tract infections, gastrointestinal infections, keratitis, otitis media, and bacteremia. P. aeruginosa is the fourth most common nosocomial pathogen, accounting for approximately 10% of hospital-acquired infections (www.cdc.gov). Immunocompromised patients, such as those undergoing cancer treatment or those infected with AIDS, burn patients, or cystic fibrosis (CF) patients, are susceptible to P. aeruginosa infections. These infections are difficult to treat by using conventional antibiotic therapies, and hence result in significant morbidity and mortality in such patients. The recalcitrant nature of P. aeruginosa infections is thought to be due to the organism's intrinsic antibiotic resistance mechanisms and its ability to form communities of bacteria encased in an exopolysaccharide matrix; such communities are known as biofilms.
P. aeruginosa possesses an impressive arsenal of virulence factors to initiate infection and persist in the host. These include secreted factors, such as elastase, proteases, phospholipase C, hydrogen cyanide, exotoxin A, and exoenzyme S, as well as cell-associated factors, such as lipopolysaccharide (LPS), flagella, and pili. The expression of these factors is tightly regulated. Many factors are expressed in a cell-density-dependent manner known as quorum sensing (QS). Quorum sensing, or cell-to-cell communication, is a means by which bacteria can monitor cell density and coordinate population behavior. The behavior was first identified in Vibrio fischeri as a mechanism to induce bioluminescence (20).
2 - Quorum Sensing and Microbial Biofilms
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- By Teresa R. de Kievit, Department of Microbiology, University of Manitoba, Winnipeg, Manitoba, Canada, Barbara H. Iglewski, Department of Microbiology and Immunology, University of Rochester School of Medicine and Dentistry, Rochester, New York, USA
- Edited by Michael Wilson, University College London, Deirdre Devine, Leeds Dental Institute, University of Leeds
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- Book:
- Medical Implications of Biofilms
- Published online:
- 23 November 2009
- Print publication:
- 01 September 2003, pp 18-35
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- Chapter
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Summary
INTRODUCTION
For a long time bacteria were believed to exist as unicellular organisms; however, it is now realized that in nature bacteria are more often found clustered in communities. Within these communities, bacteria are capable of coordinated activity through the use of a sophisticated intercellular communication mechanism called quorum sensing (QS). The capacity to behave collectively as a group has obvious advantages, for example, migration to a more suitable environment/better nutrient supply or adopting a more favourable mode of growth such as sporulation. Recently, QS was discovered to play a role in the formation of biofilms. This latter phenomenon will be the focus of this chapter as we review our current understanding of how QS affects the complex processes of biofilm development. With respect to intercellular communication and biofilms, Pseudomonas aeruginosa is one of the most intensely studied organisms, and therefore, much of this chapter will concentrate on this bacterium.
QUORUM SENSING
QS exists in both Gram-positive and Gram-negative bacteria with obvious differences between the two systems (for reviews, see Dunny and Leonard, 1997; Fuqua, Winans, and Greenberg, 1996). Here, we will focus on Gram-negative bacteria, where the two primary components of QS systems are the autoinducer (AI) signal molecule and the transcriptional activator, or R-protein. In general, the ‘language’ used for intercellular communication is based on small, diffusible, self-generated signal molecules called AIs.