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

interesting result is that the ∆PAPI-1∆PAPI-2 is less virulent than PAO1, a strain
that lacks both PAPI-1 and PAPI-2. In fact in terms of virulence PAO1 is similar to
∆PAPI-2. The differences in virulence are reflected in recovered CFU numbers
from tissue, symptom scores, survival times and histopathology, but not readily
apparent from the immune profile.
4.6 Discussion
This project was to investigate the contribution of PAPI-1 and PAPI-2 to the
virulence of Pseudomonas aeruginosa PA14 in a murine acute respiratory model by
comparing wild-type PA14 and three isogenic mutants. The project shows that both
pathogenicity islands contribute significantly to the virulence of PA14 and the loss
of both pathogenicity islands results in a severely attenuated strain. Mice infected
with the attenuated strain rather than the wild-type have an increased survival time
from 18 hours to 72 hours (70%) to surviving the experiment (30%). Eighteen hours
post-infection the CFU numbers recovered are drastically reduced in the lungs,
nasopharynx and blood compared to wild-type, PA14, also a reduction in symptom
score was only noted when both PAPI-1 and PAPI-2 are absent from PA14.
This section is going to discuss the role PAPI-1 and PAPI-2 play in virulence with
respect to the project data and the available literature. This is followed by evaluating
the hypothesis raised by He et al. (2004) regarding the differences in virulence
between PAO1 and PA14. The final discussion point will about the immune
response during P. aeruginosa infection.
4.6.1 The role of PAPI-1 during acute respiratory infection
The data generated during project demonstrated that PAPI-1 has a role in acute
respiratory infection. ∆PAPI-1 did not show a reduction in virulence compared to
PA14. The bacterial numbers recovered from the nasopharynx, lungs and blood
were insignificantly different (P