Pseudomonas aeruginosa
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CHAPTER 3.3.22 sanomoduesP
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Pseudomonas aeruginosa TIMOTHY L.YAHR AND MATTHEW R. PARSEK
The Gram-negative bacillus Pseudomonas aeruginosa is a remarkably adaptable organism. Endowed with a large repertoire of metabolic pathways, P. aeruginosa is able to adapt, survive and persist under a broad range of environmental conditions. Equipped with an equally large repertoire of pathogenic mechanisms, P. aeruginosa is capable of infecting eukaryotic organisms ranging from social amoeba to humans. The discussion in this chapter will highlight the metabolic and pathogenic diversity of P. aeruginosa and the relationship to human infection.
Cellular Biology and Basic Physiology Pseudomonas aeruginosa was first isolated from a variety of environmental sources by Schroeter in 1872 (Palleroni, 1984). Taxonomy based on 16S rRNA sequences positions P. aeruginosa within the class of Gammaproteobacteria and the family Pseudomonadaceae. Like all members of this family, P. aeruginosa is metabolically versatile and utilizes over 80 organic compounds as energy and carbon sources (Palleroni, 1984). The organism utilizes the Entner-Doudoroff pathway instead of glycolysis to oxidize sugars including fructose, galactose, glucose and xylose, is oxidase positive, and can grow at temperatures up to 42°C (Palleroni, 1984). Though P. aeruginosa is classified as an obligate aerobe, some strains will grow anaerobically by denitrification. ATP can also be generated anaerobically by fermentation of arginine and pyruvate (Vander Wauven et al., 1984; Eschbach et al., 2004). One important consequence of this metabolic diversity is that P. aeruginosa is pervasive throughout the hospital setting and persists in respiratory equipment, sinks, tubs and weak antiseptic solutions. This characteristic undoubtedly contributes to the opportunistic nature of P. aeruginosa infections. The colony morphology, pigmentation, and motility properties of P. aeruginosa strains can be quite heterogeneous. The prototypical colony is large and smooth with an elevated center giving it the appearance of a fried egg (Palleroni, 1984). Variants with alterations in colony mor-
phology arise during biofilm growth, following exposure to environmental and antibiotic stresses, and during chronic infections of the human airways (Sheehan et al., 1982; Haussler et al., 1999; Haussler et al., 2003; Deziel et al., 2001; Drenkard and Ausubel, 2002; Boles et al., 2004; Von Gotz et al., 2004). Many colony morphology variants also display phenotypic alterations in antibiotic resistance, motility, virulence gene expression, adherence properties, and biofilm formation. The generation of variants with diverse phenotypic properties may contribute to the persistence and pathogenic success of P. aeruginosa. P. aeruginosa colonies are commonly pigmented and in fact the species designation, derived from aeruginous meaning “the color of copper rust,” reflects the characteristic bluegreen color imparted on colonies by the phenazine pigment pyocyanin. Pyocyanin is a redox-active compound with m
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