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5 The role of quorum-sensing in the virulence of Pseudomonas ...

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Abstract<br />

<strong>Pseudomonas</strong> aerug<strong>in</strong>osa is an opportunistic pathogen and usually targets<br />

immunocompromised patients such as burn victims and patients with AIDS, cancer<br />

or cystic fibrosis (CF). Acquisition <strong>of</strong> this organism is associated with high<br />

mortality and can cause death with<strong>in</strong> 24 hours. <strong>The</strong> ma<strong>in</strong> <strong>the</strong>mes covered with<strong>in</strong> this<br />

<strong>the</strong>sis are pathogenicity island characterisation <strong>in</strong> vitro and <strong>in</strong> vivo as well as<br />

<strong>in</strong>vestigation <strong>of</strong> <strong>in</strong> vivo <strong>virulence</strong> <strong>of</strong> P. aerug<strong>in</strong>osa. <strong>The</strong> rationale beh<strong>in</strong>d this focus<br />

is that 10-20% <strong>of</strong> <strong>the</strong> P. aerug<strong>in</strong>osa genome is variable between stra<strong>in</strong>s and large<br />

variable regions such as genomic (pathogenicity) islands are considered more likely<br />

to contribute to <strong>the</strong> differences <strong>in</strong> disease-caus<strong>in</strong>g ability between stra<strong>in</strong>s.<br />

<strong>The</strong> first project covers <strong>the</strong> development <strong>of</strong> a novel generic yeast-based genomic<br />

island capture method, which enables a complete genomic island to be present<br />

with<strong>in</strong> a clon<strong>in</strong>g vector. It was used <strong>in</strong> <strong>the</strong> characterisation <strong>of</strong> genomic islands <strong>in</strong><br />

both P. aerug<strong>in</strong>osa and Escherichia coli. A novel genomic island <strong>in</strong> E. coli was<br />

captured and characterised.<br />

<strong>The</strong> second project <strong>in</strong>vestigates <strong>the</strong> contribution <strong>of</strong> two pathogenicity islands, PAPI-<br />

1 and PAPI-2 to <strong>the</strong> <strong>in</strong> vivo <strong>virulence</strong> <strong>of</strong> P. aerug<strong>in</strong>osa PA14. Three pathogenicity<br />

island deletant isogenic mutants were tested for <strong>virulence</strong> <strong>in</strong> a mur<strong>in</strong>e acute<br />

respiratory model <strong>of</strong> <strong>in</strong>fection developed for this project. <strong>The</strong> results showed that<br />

both pathogenicity islands contribute to <strong>virulence</strong>, but <strong>the</strong> presence <strong>of</strong> PAPI-2 is<br />

enough to ma<strong>in</strong>ta<strong>in</strong> wild-type <strong>virulence</strong>.<br />

<strong>The</strong> third project covers <strong>the</strong> exploration <strong>of</strong> <strong>the</strong> <strong>role</strong> <strong>of</strong> <strong>quorum</strong>-<strong>sens<strong>in</strong>g</strong> <strong>in</strong> <strong>the</strong><br />

<strong>virulence</strong> <strong>of</strong> P. aerug<strong>in</strong>osa LES; one <strong>of</strong> <strong>the</strong> transmissible epidemic stra<strong>in</strong>s and <strong>the</strong><br />

most common stra<strong>in</strong> recovered from CF patients across <strong>the</strong> UK. <strong>The</strong> project<br />

assessed whe<strong>the</strong>r over-expression <strong>of</strong> <strong>quorum</strong>-<strong>sens<strong>in</strong>g</strong> products is a reliable <strong>in</strong>dicator<br />

<strong>of</strong> <strong>in</strong>creased <strong>virulence</strong> with<strong>in</strong> a mur<strong>in</strong>e acute respiratory model <strong>of</strong> <strong>in</strong>fection. <strong>The</strong><br />

results showed <strong>in</strong> general, over-express<strong>in</strong>g mutants were more virulent than<br />

deficient mutants, but <strong>the</strong>re was one exception, LESB58.<br />

ii

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