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

in PAO1(Lee et al. 2006). They showed that PA14 had 58 additional gene clusters
than PAO1. They tried to analyse these 58 gene clusters in two ways. Firstly, they
screened 20 P. aeruginosa strains (including PA14 and PAO1) and compared them
for virulence in a C. elegans model of infection and ranked their virulence. They
then analysed the strains for the presence of the identified PA14-specific gene
regions. The results showed no correlation between virulence and the presence of
the PA14-specific gene regions. A second approach taken was to create a transposon
insertion mutant library for PA14. They screened the library using the C. elegans
model of infection for those in the PA14-specific gene regions for attenuation. They
discovered 9 genes, 2 of which are present in PAPI-1 that caused attenuation. The
present of these regions within the other P. aeruginosa strains, showed no set trend
for correlation for virulence within C. elegans model of infection. This led the
group to conclude that the presence of these gene regions within another P.
aeruginosa strain was not an indicator of its virulence within a C. elegans model of
infection.
The publication by Lee et al. (2006) justify the need to create P. aeruginosa
pathogenicity islands mutants. To evaluate the true impact of a pathogenicity island,
it is essential to remove the whole island. Pathogenicity islands have evolved over
time to become single elements that encode all the genes that are required to
increase virulence. The island has evolved and continued to function as a single
element because it functions better as a whole. Lee et al. (2006) discovered 9 genes
that were important for virulence in a C. elegans model of infection, 2 of which
were in PAPI-1. The data could represent ‘kinks in the armour’ of the pathogenicity
island that causes the whole island to be rendered non-functional. The availability of
the technique to create unmarked mutants within P. aeruginosa is available and our
laboratory has proven that 100kb of genome can be successfully removed. This
could be used to explore the roles of the 58 clusters of PA14-specific regions within
the strain by removing them directly, especially as so few genes within the PA14-
specific regions have an assigned function; 63% have unknown function (Lee et al.
2006). The use of PA14-specific region mutants could be used as a cost-effective
method to decide on individual genes to target for further virulence characterisation.
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