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Infection and Immunity, December 2004, p. 6836-6845, Vol. 72, No. 12
0019-9567/04/$08.00+0     DOI: 10.1128/IAI.72.12.6836-6845.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Modulation of Swarming and Virulence by Fatty Acids through the RsbA Protein in Proteus mirabilis

School and Graduate Institute of Medical Technology,¹ Graduate Institute of Microbiology College of Medicine, National Taiwan University,² Department of Laboratory Medicine, National Taiwan University Hospital, Taipei, Taiwan, Republic of China³

Received 8 May 2004/ Returned for modification 17 June 2004/ Accepted 20 August 2004

After sensing external signals, Proteus mirabilis undergoes a multicellular behavior called swarming which is coordinately regulated with the expression of virulence factors. Here we report that exogenously added fatty acids could act as signals to regulate swarming in P. mirabilis. Specifically, while oleic acid enhanced swarming, some saturated fatty acids, such as lauric acid, myristic acid, palmitic acid, and stearic acid, inhibited swarming. We also found that expression of hemolysin, which has been shown to be coordinately regulated with swarming, was also inhibited by the above saturated fatty acids. Previously we identified a gene, rsbA, which may encode a histidine-containing phosphotransmitter of the bacterial two-component signaling system and act as a repressor of swarming and virulence factor expression in P. mirabilis. We found that while myristic acid, lauric acid, and palmitic acid exerted their inhibitory effect on swarming and hemolysin expression through an RsbA-dependent pathway, the inhibition by stearic acid was mediated through an RsbA-independent pathway. Biofilm formation and extracellular polysaccharide (EPS) production play an important role in P. mirabilis infection. We found that RsbA may act as a positive regulator of biofilm formation and EPS production. Myristic acid was found to slightly stimulate biofilm formation and EPS production, and this stimulation was mediated through an RsbA-dependent pathway. Together, these data suggest that fatty acids may act as environmental cues to regulate swarming and virulence in P. mirabilis and that RsbA may play an important role in this process.

Editor: D. L. Burns

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