Background: Gram-negative bacteria that are resistant to all classes of antibiotics are now frequently isolated. Consequently, there is an urgent requirement to develop new antibiotics that target these pathogens. Pyocins are narrow-spectrum, proteinaceous antibiotics produced by Pseudomonas aeruginosa for intraspecies competition. Pyocins are known to actively translocate across the outer membrane (OM) of P. aeruginosa by parasitising iron uptake pathways. Although the mechanism of this translocation remains unclear, pyocins show exceptional potency in vitro. The extreme potency and targeted action of pyocins suggests they could be developed into clinically useful antibiotics targeted against P. aeruginosa.
Results: We show that pyocins display sub-µM efficacy against a range of P. aeruginosa isolates in a murine model of acute P. aeruginosa lung infection. These large protein antibiotics are stable in the lung environment, poorly immunogenic and their efficacy is maintained in the presence of pyocin-specific antibodies. Additionally, from mutational, structural and biophysical studies we propose a model for pyocin translocation: 1) pyocins bind to the common polysaccharide antigen (CPA) of P. aeruginosa lipopolysaccharide on the cell surface. 2) CPA-binding allows pyocins to easily locate their receptors in the OM. 3) the N-termini of pyocins pass through their receptors into the periplasm where they interact with translocation machinery. 4) TonB energizes the translocation process.
Conclusions: This study is the first to demonstrate the in vivo activity and excellent therapeutic potential of pyocins. Furthermore, this study greatly improves our knowledge and understanding of how pyocins target and translocate across the OM of P. aeruginosa.