“Difficult” bacteria has chainmail to protect it from antibiotics.

Science News reveals the secret that makes Clostridium difficile infections so tough to treat – an outer barrier called “the S layer” that protects the gut bacteria like molecular chainmail:

Using X-ray crystallography and electron microscopy, structural microbiologist Paula Salgado of Newcastle University in England and colleagues zeroed in on the main protein that makes up C. difficile’s S-layer, called SlpA. The closeup view revealed tightly linked proteins with minuscule gaps that looked like medieval knights’ chain mail. Because the gaps are so small, few molecules (such as antibiotics) can pass through. C. diff’s outer barrier is “flexible, but strong at the same time,” Salgado says.

Removing a region of the S-layer called D2 made C. diff cells susceptible to lysozyme, an enzyme typically found in saliva that tears open microbes’ exteriors, the team found.

Understanding how SlpA forms the S-layer could help researchers find new ways — such as poking holes in its chain mail — to treat C. difficile infections, which can come back time and time again.

You can read more of Salgado’s research here, in Nature Communications.