5 The role of quorum-sensing in the virulence of Pseudomonas ...
5 The role of quorum-sensing in the virulence of Pseudomonas ...
5 The role of quorum-sensing in the virulence of Pseudomonas ...
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4.6.2 <strong>The</strong> <strong>role</strong> <strong>of</strong> PAPI-2 dur<strong>in</strong>g acute respiratory <strong>in</strong>fection<br />
A reduction <strong>in</strong> <strong>virulence</strong> <strong>in</strong> PA14 was only seen when PAPI-2 was deleted, mutants<br />
∆PAPI-2 and ∆PAPI-1∆PAPI-2. <strong>The</strong> only genes highlighted <strong>in</strong> PAPI-2 with<strong>in</strong> <strong>the</strong><br />
literature as contribut<strong>in</strong>g to <strong>virulence</strong> are ExoU which is a potent cytotox<strong>in</strong> plus<br />
SpcU its chaperone. <strong>The</strong> literature appears to suggest that <strong>the</strong> majority <strong>of</strong> <strong>the</strong><br />
reduction <strong>in</strong> <strong>virulence</strong> could be due to <strong>the</strong> loss <strong>of</strong> ExoU.<br />
ExoU has been previously been shown to be an important factor <strong>in</strong> terms <strong>of</strong> acute<br />
respiratory illness with<strong>in</strong> mur<strong>in</strong>e acute respiratory models (Allewelt et al. 2000,<br />
Schulert et al. 2003, Shaver, Hauser 2004). Allewelt et al, 2000 reported a clear<br />
difference <strong>in</strong> LD50 for a panel <strong>of</strong> P. aerug<strong>in</strong>osa stra<strong>in</strong>s between those express<strong>in</strong>g<br />
ExoU and those stra<strong>in</strong>s that did not and that <strong>in</strong>troduc<strong>in</strong>g <strong>the</strong> exoU gene with its<br />
chaperone spcU <strong>in</strong>to a non-carry<strong>in</strong>g stra<strong>in</strong> could significantly reduce <strong>the</strong> LD50. <strong>The</strong><br />
loss <strong>of</strong> ExoU from <strong>the</strong> P. aerug<strong>in</strong>osa stra<strong>in</strong>, PA99, was also shown to be<br />
significantly attenuated <strong>in</strong> a mur<strong>in</strong>e acute respiratory model (Shaver, Hauser 2004).<br />
This model is very similar to <strong>the</strong> one described <strong>in</strong> this <strong>the</strong>sis, <strong>the</strong>y used a similar<br />
dose and cull<strong>in</strong>g timepo<strong>in</strong>t (18 hours). <strong>The</strong>y evaluated differences <strong>in</strong> <strong>virulence</strong> by<br />
perform<strong>in</strong>g CFU counts on lung, liver and spleen homogenate. <strong>The</strong>y did not<br />
evaluate <strong>the</strong> nasopharynx or directly assess dissem<strong>in</strong>ation from <strong>the</strong> lungs to <strong>the</strong><br />
blood by cardiac puncture.<br />
<strong>The</strong> data generated dur<strong>in</strong>g this project support <strong>the</strong>se observations as <strong>the</strong>y show a<br />
loss <strong>of</strong> PAPI-2 results <strong>in</strong> an attenuated stra<strong>in</strong> <strong>in</strong> comparison with PA14. <strong>The</strong> data<br />
suggest that PAPI-2 plays a number <strong>of</strong> important <strong>role</strong>s <strong>in</strong> acute respiratory <strong>in</strong>fection.<br />
Infection with ∆PAPI-2 <strong>in</strong> comparison with wild-type PA14 led to a loss <strong>of</strong> one log<br />
<strong>in</strong> nasopharynx as well as <strong>the</strong> lungs and a two log <strong>in</strong> blood at 18 hours post-<br />
<strong>in</strong>fection. Consideration <strong>of</strong> <strong>the</strong> data generated for ∆PAPI-1, suggests that <strong>the</strong><br />
presence <strong>of</strong> PAPI-2 solely is enough to ensure persistence <strong>in</strong> nasopharynx and lungs<br />
as well as successful dissem<strong>in</strong>ation to <strong>the</strong> blood. This data is <strong>the</strong> first to recognise<br />
that PAPI-2 is important for upper respiratory tract (nasopharynx) <strong>in</strong>fection.<br />
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