Time to wrap up this series, for now. Let’s finish with three bacteria: Faecalibacterium prausnitzii, Escherischia coli, and Clostridium difficile. The good, the bad, and the ugly.
Everybody has heard of E Coli; beaches are closed to swimming because of high coliform counts. This gives the impression that it is the main bacteria found in feces, but that’s far from the case. They make up less than one percent of the mix, but they are easy to culture. Their presence in a water or food sample indicate fecal contamination, but they are usually harmless. Usually; but the group includes the nasty O157:H7 variant, a relatively recent arrival that incorporates some genes from the Shigella bacteria. Feedlots may be where these genes were acquired, giving rise to hamburger disease and the Walkerton crisis. If Theodor Escherisch came back, he would not recognize his formerly innocuous bacteria.
C-diff, Clostridium difficile, became notorious in the early 2000s. Virulent strains in hospitals in Quebec and Alberta killed several patients in 2003, and over 100 have died in Canada alone since. This is an infection contracted via the oral-fecal route (yes, they like our gut) that causes fever, diarrhea, and sepsis. This ugly critter likes to colonize the guts of people who have been treated with antibiotics; like a weed, they colonize the empty gut faster than other bacteria. (Surprisingly, it owes its name not to the difficulties it causes but to the fact that it is very fastidious and difficult to culture.)
But where there are villains is bound to be a hero. Faecalibacterium prausnitzii is one of these. Moises Velasquez-Manoff wrote a really interesting article on how this particular bug was identified and its positive role in the gut realized:
In the mid-2000s Harry Sokol, a gastroenterologist at Saint Antoine Hospital in Paris, was surprised by what he found when he ran some laboratory tests on tissue samples from his patients with Crohn’s disease, a chronic inflammatory disorder of the gut. The exact cause of inflammatory bowel disease remains a mystery. Some have argued that it results from a hidden infection; others suspect a proliferation of certain bacteria among the trillions of microbes that inhabit the human gut. But when Sokol did a comparative DNA analysis of diseased sections of intestine surgically removed from the patients, he observed a relative depletion of just one common bacterium, Faecalibacterium prausnitzii. Rather than “bad” microbes prompting disease, he wondered, could a single “good” microbe prevent disease?
F. praustnitzii is one of the more common bacteria in the human gut, and its relative absence has been associated with Crohn’s disease, but also with obesity, asthma, and depression – not bad for a single type of bacteria. And yes, they like dietary fiber, please.
What is surprising to be is how similar this particular bacterium is to several black sheep in its cluster class, Clostridium IV. This includes the various clostridia that cause botulism, gas gangrene, and tetanus. There is still so much to learn about our very own bacteria. Don’t be surprised if you’re asked for fecal samples more often in the future.
This is the final post of this microbiome series. The previous post, on gut bacteria and asthma, can be found here.