Clostridium difficile can invade your guts like a colonizing horde, but if your native good bacteria work together, they stand a chance.

It’s a tale perfect for Hollywood: Faced with a powerful and destructive invader, individually weaker natives pool their talents to successfully defend their homes, though some sacrifice their lives to do so. If you have a gut feeling you've experienced this before, it's because it happens regularly in our intestines.

Unlike films, bacterial battles do not always go to script, which is why you sometimes find yourself with your head over the toilet bowl as microbial invaders do their worst. University of Michigan researchers are working to explain why some communities of “good bacteria” fight off invaders while others succumb.

In mBIO, Dr. Patrick Schloss reports on the circumstances that allow bacterial ecosystems in mice to fight off Clostridium difficile, the aptly named spore-forming bacterium that kills 14,000 Americans a year. Most victims are taking antibiotics that weaken the capacity of their healthy bacteria to protect intestinal territory.

In the new study, Schloss and colleagues demonstrate the capacity of different combinations of bacteria to prevent C. difficile from taking hold. They report that "C. difficile resistance was never attributable to a single organism, but rather it was the result of multiple microbiota members interacting in a context-dependent manner.”

The authors are unable to explain all the variation in observed infection rates. However, they learned enough to predict 77% of the concentration of C. difficile in the droppings of the unfortunate mice 24 hours after they were given doses of the invasive species.

“We observed that populations associated with the Porphyromonadaceae, Lachnospiraceae, Lactobacillus, and Alistipes were protective,” the authors report. Like any such film, there are a few traitors as well, with the authors adding, “Populations associated with Escherichia and Streptococcus were associated with high levels of colonization.”

The trickster is Akkermansia, which either helps or hinders the invaders depending on circumstances. We’ll just call that one Jack Sparrow, shall we?

"We know that individual humans all have different collections of gut bacteria, that your internal 'village' is different from mine. But research has mostly focused on studying one collection at a time," says Schloss. "It's the community that matters, and antibiotics screw it up. By looking at many types of microbiomes at once, we were able to tease out a subset of bacterial communities that appear to resist C-diff colonization, and predict to what extent they could prevent an infection."

The authors hope that, by taking samples of patients’ fecal bacteria, doctors will be able to work out who is most at risk of lethal intestinal infections. Potentially, it may become possible to provide transplants of only those bacteria under-represented in an individual’s gut.

It can’t be assumed that the bacterial combination that works best in mice is also ideal for humans, but Schloss believes the testing techniques his team have pioneered will serve well in establishing humans’ most resilient bacterial team.

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