Pathak, Aditi
(2012)
New vaccines for infectious diseases: immunological targeting of the quorum sensing system of Pseudomonas aeruginosa.
PhD thesis, University of Nottingham.
Abstract
Pseudomonas aeruginosa is an opportunistic pathogen of animals and humans causing medical complications in burns, wounds, and cystic fibrosis. P. aeruginosa is efficient at adapting its virulence phenotype depending on the site of infection. Emerging multi-drug resistant strains and a limited number of effective anti-pseudomonal antibiotics renders P. aeruginosa infections increasingly difficult to treat.
To address this need, this thesis considers targeting bacterial quorum sensing, which regulates the production of virulence factors, as an alternative prophylactic strategy. The P. aeruginosa quorum sensing system is compromised of three interlinked but independent systems, Las, Rhl and Pqs, which produce and utilise quorum sensing system molecules, 3OC12-HSL, C4-HSL and PQS respectively. Immunological targeting of the quorum sensing system molecule 3OC12-HSL, through active immunisation (vaccines), inhibits the Las system, resulting in a longer life expectancy in mice infected with P. aeruginosa in vivo.
However, P. aeruginosa has the capacity to develop resistance, through compensatory mechanisms, towards quorum sensing inhibition that targets the Las system only. This emphasises the need to target all three quorum sensing systems, Las, Rhl, and the Pqs, in order to inhibit quorum sensing. The present study focuses particularly on the development of a multi-component anti-quorum sensing system vaccine that would target the three main quorum sensing system molecules, effectively compromising the quorum sensing system and minimising compensatory mechanisms.
This involved the synthesis of haptens based on the quorum sensing system molecules, which were used to haptenise the immunogenic carrier keyhole limpet haemocyanin. Syntheses of the haptens, AP1 (derivative of 3OC8-HSL) and AP2 (derivative of PQS), were conducted using adapted published methods. The resulting conjugates, AP1-keyhole limpet haemocyanin and AP2-keyhole limpet haemocyanin were immunogenic in mice and rabbits. The specific anti-hapten polyclonal antibodies that were generated demonstrated cross-reactivity with the natural quorum sensing system molecules of P. aeruginosa that translated in significant and specific anti-quorum sensing system molecule activity in bioluminescence reporter assays. Anti-AP1 polyclonal antibodies were able to reduce biofilm formation at high concentrations, however, significant reduction of biofilm formation was seen when the anti-hapten antibodies were used in combination.
In this study, it has been demonstrated that the inhibition of the quorum sensing system should include the three systems, Las, Rhl and PQS, and that this can be done by a multi-component anti-quorum sensing system vaccine. These data suggest that a multi-component anti-quorum sensing system vaccine takes us a step forward to a viable prophylaxis against P. aeruginosa for susceptible patients.
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