The role of the Rab32/BLOC3 host defence pathway in controlling Staphylococcus aureus infections

Supervisors: Dr Massimiliano Baldassarre, Prof Stefania Spanò, Prof Ross J Fitzgerald

Project Description:

S. aureus is an emerging problem in animal agriculture and veterinary medicine and our recent studies have shown how livestock could represent a source of pathogenic S. aureus (1) with the potential to spread in human populations.

We have recently discovered an antimicrobial traffic pathway that prevents the survival of Salmonella Typhi, the agent of typhoid fever, in mouse macrophages. Central components of this pathway are the small GTPase Rab32 and its guanine nucleotide exchange factor BLOC3 (2,3).

Our hypothesis is that this pathway is also critical for the killing of S. aureus and it may be responsible for the virulence and host-specificity of different S. aureus strains. S. aureus may have evolved strategies to neutralise this pathway gaining the ability to survive inside specific host immune cells and therefore increasing their pathogenic potential.

In this project we will test the above hypothesis pursuing the following aims.

We will:
1)    Test a range of S. aureus strains, of both human and animal origin, for their sensitivity to the RAB32/BLOC-3 pathway. Specifically, we will answer the following questions: 1) Is there any correlation between virulence and the RAB32/BLOC-3 pathway sensitivity? 2) Is there any molecular evidence that can explain any difference in susceptibility?

2)    Study the interaction of S. aureus with macrophages from different species. Specifically, we will answer the following questions: 1) Do the bacteria actively invade the macrophages? 2) How they survive inside the macrophages? 3) Is there any host restriction/specificity? If so, is the restriction/specificity depending on host or bacterial factors?

Dr Baldassarre has an extensive molecular biology expertise in fields such as adhesion receptors and actin cytoskeleton. Those are cellular systems crucial for macrophage phagocytosis and microbial killing. They are also systems hijacked during S. aureus infection. Prof Stefania Spanò is an expert in microbe-host interaction and Prof Fitzgerald is an expert of S. aureus pathogenicity and uses a range of molecular and genomic tools to understand the origin and evolution of S. aureus infection in human and livestock.

The presence of three supervisors with both overlapping and complementary expertise will ensure that the student will receive a full guidance throughout the project. It will also guarantee a first-class training in a range of techniques such as:

- microbial techniques including molecular biology, bacterial physiology, sterile technique, growth and culture of microorganisms;
- molecular techniques such as PCR, cloning, creation of gene knockouts (including CRISPR/Cas9); mammalian cell cultures and S. aureus infection;
- microscopy techniques including fluorescent wide field and confocal microscopy, live imaging and 3D reconstruction.

1)    Spoor LE, McAdam PR, Weinert LA, Rambaut A, Hasman H, Aarestrup FM, Kearns AM, Larsen AR, Skov RL, Fitzgerald JR. Livestock Origin for a Human Pandemic Clone of Community- Associated Methicillin-Resistant Staphylococcus aureus mBio (2013) vol. 4 no. 4 e00356-13.
2)    Spanò S, Galán JE. A Rab32-dependent pathway contributes to Salmonella typhi host restriction. Science. (2012) 338:960-3.
3)    Spanò S, Gao X, Hannemann S, Lara-Tejero M, Galán JE.  A Bacterial Pathogen Targets a Host Rab-Family GTPase Defense Pathway with a GAP. Cell Host Microbe. (2016) 19(2):216-26.

To apply for this project, please go to this link.