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Chapter 4 : Quorum Sensing
This chapter focuses on quorum sensing in gram-negative bacteria with a special emphasis on the well-studied intercellular communication network found in Pseudomonas aeruginosa. At least 22 gram-negative species have been shown to utilize an acyl-homoserine lactone based quorum sensing system to control various genes, and more than 50 different species have been shown to produce an acyl-homoserine lactone type of cell-to-cell signal. One of the more well-studied pathogens in this group is P. aeruginosa, which contains two separate quorum sensing systems. The study of quorum sensing in P. aeruginosa began when it was discovered that the production of the virulence factor elastase was controlled by LasR, a homolog of LuxR. The genetic organization of the rhl quorum sensing system is also similar to the las quorum sensing system. Evidence for the importance of quorum sensing in infections was also found by randomly mutagenizing the P. aeruginosa wild-type strain PA14 in search of virulence factors. A popular theory is that delaying the production of certain virulence factors may allow P. aeruginosa to face a lesser immune response while its population builds. Biofilm formation is believed to be a critical step in the disease produced when P. aeruginosa chronically infects the lungs of patients with cystic fibrosis. The authors hope the understanding of quorum sensing will provide the background for the development of new and effective antimicrobial therapies that will provide much needed options for the treatment of bacterial infections.