Determining the prevalence of the PGA biosynthetic operon in the genus Staphylococcus and the investigation of a PGA capsule depolymerase as a novel t

Staphylococci are an important group of bacteria and are often found on the skin of humans and animals. However, some species, like methicillin resistant Staphylococcus aureus (MRSA) can cause life threatening infections. Under certain conditions, other staphylococcal species known as Coagulase-negative Staphylocci or CoNS can also cause serious infections, often in hospitals but also in important livestock animals such as cattle. Worryingly, these species are becoming increasingly resistant to antibiotics making infections harder to treat. Therefore, it is important to investigate new ways of treating these infections.

When causing an infection, these bacteria use a protective capsule or "coat" to hide from the human immune system. Additionally, it has been shown in animal models that the capsule is essential for colonisation, highlighting the importance of this virulence factor. This project aims to develop a treatment that will rapidly remove this capsule, allowing the host immune system to recognize the infection and clear the invading bacteria. This approach will have the benefit of being active against antibiotic resistant strains of CoNS.

This approach will involve the use of a capsule to remove the protective poly-gamma-glutamic acid (PGA) capsule from the surface of the bacterium strip away the protective capsule from the surface of the pathogen. We already have one such enzyme in our possession and hope develop this as a new therapy for the treatment of CoNS infections. The project will use a translational approach to test the potential of this therapy by meeting the following three key milestones/objectives:

Firstly, the prevalence and genetic diversity of the PGA biosynthetic operon within the CoNS group will be determined to identify which members represent viable targets of this capsule-stripping therapy. We will also sequence the genomes of several CoNS isolates from various sources (human and animal) to further confirm the prevalence and genetic diversity of the genes responsible for producing the capsule, especially in species infecting livestock.
Secondly, the efficacy of this approach will be tested against identified species in vitro by investigating the effect of depolymerase treatment on macrophage uptake and killing of CoNS. This will be investigated using a combination of by using a combination of epifluorescent microscopy and fluorescence-activated cell sorting (FACS).
Finally, the capacity for depolymerase therapy to resolve or prevent lethal bacteraemia will be investigated using a Galleria mellonella model of Staphylococcal infection. This model will also allow us to monitor the Galleria immune response in treated versus untreated groups by measuring the transcriptional response of key genes involved in the innate immune response using qPCR.
Successful outcomes from this project will result in a novel therapy which can be used for the treatment of both human and livestock infections caused by CoNS.