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’s 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.diff at defending itself against the antibiotics and immune system molecules sent to attack it.”