Elucidating Staphyloccoccus aureus Strategies for Survival to Antimicrobial Mechanisms

Aberdeen University  School of Medicine, Medical Sciences & Nutrition 

Application Deadline: 18 May 2018

Project Description
Bacterial infections remain a major health threat. The emergence of antimicrobial resistance has increased the risk of untreatable life-threatening infections. Staphylococcus aureus (S. aureus) is a widespread commensal bacterium and pathogen. Approximately 50% of individuals are, at least intermittently, colonized with S. aureus. S. aureus was first identified in 1880 in Aberdeen, Scotland, by surgeon Sir Alexander Ogston in pus from a surgical abscess in a knee joint of one of his patients. Today S. aureus is the most common cause of hospital-acquired infection in UK with 40-60% of these resistant to methicillin (methicillin-resistant Staphylococcus aureus, MRSA) and represent a major public health problem. In addition to being an important human pathogen, S. aureus is also an emerging problem in animal agriculture and veterinary medicine.

To become a pathogen and cause systemic infection S. aureus needs to overcome host defences such as destruction by macrophages and neutrophils. Indeed, there are indications that S. aureus can survive in macrophages but the mechanism that allow this are still unknown.

We have recently discovered an antimicrobial trafficking 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 preliminary data show that this pathway is also critical for the killing of S. aureus and it may be responsible for the virulence of different S. aureus strains. We hypothesise that S. aureus has evolved strategies to evade or neutralise this Rab32/BLOC3 pathway increasing its pathogenic potential.

This studentship project will test the above hypothesis pursuing the following aims:

(1) Test macrophage response to S. aureus infection in both normal macrophages and macrophages with an inactive Bloc3/Rab32 antimicrobial (BRAM) pathway. The transcriptional response will be determined using mRNA sequencing and quantitative RT-PCR. A combination of proteomics, biochemistry and microscopy will be used to study the cell signalling pathways activated by S. aureus in macrophages and to dissect the differences in this response in normal vs BRAM deficient macrophages; and

(2) We know that BRAM pathway components are important for intracellular trafficking and in particular for lysosomal related organelles formation. Using state-of-the-art fluorescence-lifetime microscopy the fate of the phagocytosed S aureus will be studied and how alterations in endocytic trafficking can change the ability of S aureus to survive inside the phagosomes and mechanisms involved will be defined.

These studies are important to understand the components of the defence system that can be targeted to develop new strategies to kill pathogenic bacteria and to overcome the threat posed by antibiotic resistant strains.

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. Professor Stefania Spanò is an expert in pathogen-host interaction and Dr Heather Wilson is an expert in macrophages and their immune-modulation. The supervisory team has overlapping and complementary expertise to ensure the student will receive first-class training in a range of divergent laboratory techniques and transferable skills 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;

-Primary cell culture techniques including the isolation and culture of human monocyte derived macrophages and stem cell derived macrophages and host defence systems; and

- Microscopy techniques including fluorescent wide field and confocal microscopy, live imaging and 3D reconstruction.
Funding Notes
This project is part of a competition funded by the Institute of Medical Sciences. The duration of the degree programme is four years (48 months) and full funding is available to UK/EU applicants only.

Candidates should have (or expect to achieve) a minimum of a 2.1 Honours degree in a relevant subject. Applicants with a minimum of a 2.2 Honours degree may be considered provided they have a Merit/Commendation/Distinction at Masters level.

Please apply for admission to the 'Degree of Doctor of Philosophy in Medical Sciences (Science)' to ensure that your application is passed to the correct school for processing.

References
(1) H.F. Wertheim, D.C. Melles, M.C. Vos, W. van Leeuwen, A. van Belkum, H.A. Verbrugh, J.L. Nouwen. The role of nasal carriage in Staphylococcus aureus infections. Lancet Infect Dis, 5 (2005), pp. 751-762.

(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.