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J. Bacteriol. doi:10.1128/JB.01659-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Swarming of Pseudomonas aeruginosa is a complex adaptation leading to increased production of virulence factors and antibiotic resistance

Centre for Microbial Diseases & Immunity Research, University of British Columbia, 2259 Lower Mall, Vancouver BC, Canada

^* To whom correspondence should be addressed. Email: joerg{at}cmdr.ubc.ca.

	Abstract

In addition to swimming and twitching motility, Pseudomonas aeruginosa is able to swarm on semi-solid (viscous) surfaces. Recent studies have indicated that swarming is a more complex type of motility influenced by a large number of different genes. To investigate the adaptation process involved in swarming motility, gene expression profiles were analyzed by performing microarrays on bacteria from the leading edge of a swarm zone, compared to bacteria growing in identical medium under swimming conditions. Major shifts in gene expression patterns were observed under swarming conditions including, among others, the over-expression of a large number of virulence-related genes such as those encoding the type III secretion system and its effectors, extracellular proteases, and iron transport. In addition, swarming cells exhibited adaptive antibiotic resistance against polymyxin B, gentamicin and ciprofloxacin compared to their planktonic (swimming) counterparts. By analyzing a large subset of upregulated genes, we were able to show two virulence genes, lasB and pvdQ, were required for swarming motility. These results clearly favoured the conclusion that swarming of P. aeruginosa is a complex adaptation process in response to a viscous environment resulting in a substantial change in virulence gene expression and antibiotic resistance.

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