Teasing out the mechanisms of biofilm formation for the treatment of S. aureus infections on indwelling devices: the role of the surface protein SdrC

Antibiotic resistance has become a great challenge in the healthcare setting. In particular antibiotic resistant strains of Staphylococcus aureus pose further challenges. Methicillin resistant S. aureus (MRSA) is widespread in healthcare facilities and in the wider community and multi-drug resistant strains have been identified. S. aureus is normally present on the surface of the skin where it causes no harm. However, it can easily colonize open wounds causing infection. Systemic infections can result from these wound infections leading to severe problems such as sepsis and infective endocarditis. Infection after surgical implantation of devices, such as joint replacements, can result in the formation of biofilms coating the devices that are difficult to treat. Biofilms are an accumulation of bacteria on a surface which often persist as most antibiotics do not easily penetrate them. In biofilms, bacteria interact directly with the foreign surface, with host proteins coating the surface and can also accumulate through interactions directly with each other.

Thus, there are multiple mechanisms involved in biofilm formation. It is important to fully understand all the mechanisms of biofilm formation in order to be able to disrupt their formation and persistence. In our recent paper, we have characterized the direct binding interaction (cell-cell adhesion) through the S. aureus surface protein, serine-aspartate repeat protein C (SdrC). Our study also reveals the mechanism of interaction between SdrC and inert surfaces. Furthermore, we have demonstrated how a small peptide can be used to block these interactions preventing biofilm formation suggesting a possible approach that could be used to treat SdrC dependent S. aureus biofilms. This study is the result of a multi-disciplinary collaboration across research institutes in Ireland and Belgium with Dr. Brennan (RCSI) contributing to the molecular modelling, Prof. Joan Geoghegan, Prof. Timothy Foster and Leanne Hayes (Trinity College Dublin) leading the molecular biology and microbiological functional studies and researchers from University Catholique de Louvain characterizing the interactions quantitatively using atomic force microscopy.

Marian Brennan

More details can be found in “Molecular interactions and inhibition of the staphylococcal biofilm-forming protein SdrC”.

 

MCT researchers shed light on the ancestry of the Irish Travellers from the perspective of DNA

Edmund Gilbert reports

A new study, led by Prof. Gianpiero Cavalleri at MCT and Prof. Jim Wilson at the University of Edinburgh, has examined the population history of the Irish Travellers and has confirmed that the Irish Travellers share a common Irish origin with the settled Irish population. The work has also for the first time estimated the date which this divergence occurred.

A roadside camp in County Mayo 1972. Courtesy of George Gmelch

The Irish Travellers are a small nomadic population, making up about 0.6% of the total population on the island of Ireland, or between 29,000 and 40,000 individuals. Within the population cousin marriages (consanguineous marriages) are common, and the population is socially isolated from the surrounding settled Irish population.
The researchers, who also include MCT PhD student Edmund Gilbert, Shai Carmi of the Hebrew University of Jerusalem, and Sean Ennis of University College Dublin, used SNP-array based genotype data to compare the population genetics of the Irish Travellers to neighbouring Irish and British populations, as well as world-wide groups and European Roma Gypsies.
The study found that although the Irish Travellers were genetic closest to the settled Irish population, they showed significant differences. The study also confirmed the lack of recent shared genetic ancestry between the Irish Travellers and Roma Gypsies. The Irish Travellers, therefore, represent a subset of Irish genetic diversity, and the significant differences can be attributed to genetic drift, brought on by hundreds of years of genetic isolation and a decreasing population size. The analysis showed Irish Travellers also exhibit within-population sub-structure with four apparently distinct groups emerging, and interestingly these groups mirror different forms of the Shelta language and sociological groups within the Irish Travellers.

Galway John Ward making tinware and Galway 1971. Courtesy of George Gmelch

The dating of the origin of the Irish Travellers is of considerable interest, but this is a distinct date from the genetic origins of each population. This study has estimated a time of genetic divergence of the Irish Travellers and the settled Irish population using genomic tracts of shared identity. This method estimated the divergence to about 12 generations (360 years) ago, which is far older than common belief that the Irish Traveller population arose from the time of the Great Famine. The size of the dataset limited the authors to exploring the relatively simple model of one divergence event, future work is required to expand the study to explore more complex demographic models. The Irish Traveller population was shown to have high proportions of the genome where both maternal and paternal copies are identical, at similar levels to other consanguineous populations around the world.
The research was also welcomed by author and Traveller activist, Michael McDonagh said, “As a Traveller who has spoken on the history and identity of Irish Travellers to many groups ranging from children to academics, you sometimes rely on anecdotal information in trying to put across a serious message about Irish Traveller history. I am delighted that now we have qualified evidence that substantiates the argument I have made for many years, which is that Travellers did not descend from the Famine in Ireland. This research allows us to bring Irish Traveller history back many and gives us a factual identity.”

Recent MCT Papers In High Impact Journals With Commentaries

CNV and Schizophrenia Working Groups of the Psychiatric Genomics Consortium; Psychosis Endophenotypes International Consortium. [including Waddington J]. Contribution of copy number variants to schizophrenia from a genome-wide study of 41,321 subjects. Nat Genet. 2017 Jan;49(1):27-35. PMID: 27869829

John Waddington writes about his group’s participation in a global research endeavour that has produced a series of articles in Nature, Nature Genetics and Nature Neuroscience on the pathobiology of schizophrenia The Psychiatric Genomics Consortium (PGC) unites investigators around the world to conduct meta- and mega-analyses of genome-wide genomic data on psychiatric disorders, to achieve goals that cannot be reached by individual or indeed most national programmes. Its website (www.med.unc.edu/pgc) provides information about the organization, implementation and results of the PGC. This consortium began in early 2007 and has rapidly become a collaborative confederation of investigators from 38 countries. There are samples from more than 900,000 individuals currently in analysis, and this number is growing rapidly. The PGC is the largest consortium and the largest biological experiment in the history of psychiatry.
From 2007-11, the PGC focused on several disorders, from schizophrenia through to autism, attention-deficit hyperactivity disorder, bipolar disorder and major depressive disorder. These now extend to large studies of eating disorders, substance use disorders, obsessive-compulsive disorder/Tourette’s Syndrome and post-traumatic stress disorder. Initially, the PGC focused on common single nucleotide polymorphisms (SNPs) but has expanded to include copy number variation (CNVs) and uncommon/rare genetic variation. The PGC has received funding from many sources. It has relied heavily on the goodwill of its members and their donated effort, with the establishment andgenotyping of its primary studies funded by a wide range of national, international and commercial entities.

We have been involved in the Schizophrenia Working Group of the PGC for many years, from its progenitor organisation the International Schizophrenia Consortium, primarily through substantial funding from the Wellcome Trust for five centres across the island of Ireland (one led by us) to contribute DNA from well characterised patient populations to a national dataset curated at Trinity College Dublin. This dataset has then been shared with the PGC. The resultant studies have evolved from the first investigation of CNVs in schizophrenia (3,391 cases, 3,181 controls; Nature 2008; 455: 237-41), through to the largest GWAS study on schizophrenia undertaken to date (36,989 cases, 113,075 controls; Nature 2014; 511: 421-7), to this most recent publication (21,094 cases, 20,227 controls; Nature Genetics 2017; 49: 27-35), the largest study of CNVs in schizophrenia yet undertaken. This has been, and continues to be, an exemplary, rewarding journey of global collaboration to illuminate the pathobiology of the intractable human condition that is psychotic illness.

 


Chion A, O’Sullivan JM, Drakeford C, Bergsson G, Dalton N, Aguila S, Ward S, Fallon PG, Brophy TM, Preston RJ, Brady L, Sheils, O, Laffan M, McKinnon TA, O’Donnell JS. N-linked glycans within the A2 domain of von Willebrand factor modulate macrophage-mediated clearance. Blood. 2016 Oct 13;128(15):1959-1968. PMID: 27554083.

Jamie Marie O’Sullivan writes about this study:

Von Willebrand factor (VWF) is a large multimeric plasma sialoglycoprotein that plays two critical roles in normal haemostasis. First it mediates platelet adhesion to exposed subendothelial collagen at sites of vascular injury. Second, VWF acts as a carrier molecule for procoagulant factor VIII, thereby protecting it from premature proteolytic degradation and clearance. Deficiency of either VWF (von Willebrand disease, VWD) or FVIII (Haemophilia A) is associated with a significant bleeding phenotype. Conversely, elevated plasma levels of the VWF-FVIII complex constitute a dose dependent risk factor for both venous and arterial thrombosis. Consequently, understanding the factors that determine how plasma VWF levels are regulated is not only of basic scientific interest, but also direct clinical importance.

Despite the fact that type 1 von Willebrand disease constitutes the most common inherited bleeding disorder worldwide, the mechanisms underlying the reduced plasma VWF levels in these patients is not well established. However, emerging evidence suggests that reduced circulatory half-life may be important in a significant number of patients. However the biological mechanisms underlying VWF clearance from the plasma remains elusive. Work is on-going within the group of Professor James O’Donnell to investigate the importance of specific VWF domains in modulating half-life in vivo.

In the October issue of Blood the group published novel findings demonstrating a critical role for VWF glycosylation in determining its circulatory half-life. By examining the clearance of various truncated fragments of VWF, we observed that the A domains of VWF contain a receptor-recognition site important in mediating VWF binding to macrophages in vitro, and in regulating VWF clearance by macrophages in vivo. Furthermore site-directed mutagenesis demonstrated a key role for N-linked glycan structures at position N1515 and N1574 within the A domains in protecting VWF against macrophage-mediated clearance. More specifically, the protective effect of these large complex N-linked glycan structures may be due to steric hindrance, with shielding of cryptic binding sites for macrophage clearance receptor low density lipoprotein receptor-related protein 1 (LRP1).

Defining the mechanisms underpinning VWF clearance is not only of direct translational relevance, but may also have important implications for the development of novel therapeutic agents with significant commercial appeal. For example, the estimated cost of clotting factor concentrates to the global market is predicted to exceed €10 billion per annum by 2020. It is therefore perhaps unsurprising that major pharmaceutical companies (including Baxter®, Bayer®, Novo Nordisk® and Octapharma®) are actively pursuing development of longer-acting coagulation factor products (including VWF and FVIII) as a priority. Our novel findings further scientific understanding in relation to the molecular mechanisms involved in regulating coagulation glycoprotein clearance from plasma.


McGettrick AF, Corcoran SE, Barry PJ, McFarland J, Crès C, Curtis AM, Franklin E, Corr SC, Mok KH, Cummins EP, Taylor CT, O’Neill LA, Nolan DP. Trypanosoma brucei metabolite indolepyruvate decreases HIF-1α and glycolysis in macrophages as a mechanism of innate immune evasion. Proc Natl Acad Sci U S A. 2016 Nov 29;113(48):E7778-E7787. PMID: 27856732.

Dr. Anne McGettrick and Sarah Corcoran at Trinity College Dublin lead a team of researchers including Dr. Annie Curtis (now at MCT) on a study that uncovered how the African parasites trypanosomes evade the immune system in their hosts, The biochemists have unearthed a metabolic by-product of trypanosome activity known as indolepyruvate modulates the inflammatory response of the host and evades immune detection. This discovery may offer excellent possibilities for developing anti-trypanosome drugs and therapies because inhibiting the production of indolepyruvate may be key in fighting the parasite. Full details can be found here https://www.tcd.ie/news_events/articles/solving-a-putrid-camel-pee-riddle-may-aid-millions-affected-by-sleeping-sickness/7385