New findings on the superbug C.difficile uncover the impressive structure of its protective armour for the first time.
Scientists from Newcastle, Sheffield, and Glasgow Universities have joined forces with colleagues from Imperial College and Diamond Light Source, to conduct a comprehensive research study into the superbug C.difficile.
Researchers outlined the structure of the main protein, SIpA, that forms a close-knit yet flexible outer layer that resembles chain mail, and how they arranged to form a pattern and create this flexible armour. This potentially opens the possibility of designing C.difficile specific drugs to break the protective layer and create holes to allow molecules to enter and kill the cell.
“Excitingly, it opens the possibility of developing drugs that target the interactions that make up the chain mail,” commented Dr Paula Salgado, Senior Lecturer in Macromolecular Crystallography, Newcastle University.
C.difficile is a type of bacteria that can cause diarrhoea. It often affects people who have been taking antibiotics and can usually be treated with another type of antibiotic. Common symptoms include diarrhoea, loss of appetite, and feeling sick.
The findings were published in Nature Communications.
The protective armour of C.difficile
One of the many ways that superbug C.difficile protects itself from antibiotics is a special layer that covers the cell of the whole bacteria – also known as the surface layer, or S-layer. This flexible armour acts by protecting the entry of drugs or molecules released by our immune system to fight bacteria.
The team determined the structure of the proteins, and how they were arranged, utilising a combination of X-ray and electron crystallography.
Corresponding author Dr Paula Salgado, Senior Lecturer in Macromolecular Crystallography who led the research at Newcastle University said: “I started working on this structure more than 10 years ago, it has been a long, hard journey but we got some really exciting results!”
“Surprisingly, we found that the protein forming the outer layer, SlpA, packs very tightly, with very narrow openings that allow very few molecules to enter the cells. S-layer from other bacteria studied so far tend to have wider gaps, allowing bigger molecules to penetrate. This may explain the success of C.difficile at defending itself against the antibiotics and immune system molecules sent to attack it.”
Infections are becoming challenging to treat with the rise of antibiotic resistance. Antibiotic resistance has been declared by the World Health Organization as one of the top 10 global public health threats.
Superbugs are strains of bacteria that have become resistant to antibiotic drugs. C.difficile is a superbug that infects the human gut and has become resistant to all but three drugs.
Furthermore, it becomes a problem when we take antibiotics, as the good bacteria found in the gut are killed alongside those causing an infection. Thus, as C.difficile is resistant, it can grow and cause diseases ranging from diarrhoea to death due to massive lesions in the gut. Unfortunately, the cycle restarts when the only way to treat C.difficile is to take antibiotics and the result is recurrent infections or antibiotic resistance.
Determining the structure allows the possibility of designing C.difficile-specific drugs to break the S-layer, the chainmail, and creates holes to allow molecules to enter and kill the cell.
Colleagues, Dr Rob Fagan and Professor Per Bullough at the University of Sheffield carried out the electron crystallography work.
Dr Fagan said: “We are now looking at how our findings could be used to find new ways to treat C. diff infections such as using bacteriophages to attach to and kill C. diff cells – a promising potential alternative to traditional antibiotic drugs.”
From Dr Salgado’s team at Newcastle University, PhD student Paola Lanzoni-Mangutchi, and Dr Anna Barwinska-Sendra unravelled the structural and functional details of the building blocks and determined the overall X-ray crystal structure of SlpA. Paola said: “This has been a challenging project and we spent many hours together, culturing the difficult bug and collecting X-ray data at the Diamond Light Source synchrotron.”
Dr Barwinska-Sendra concluded: “Working together was key to our success, it is very exciting to be part of this team and to be able to finally share our work.”