This Is Your Gut on Drugs

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Doctors--and many patients--know the kind of nasty gut distress that antibiotics can wreak.

Dubbed AAD, for antibiotic-associated diarrhea, the problem results when antibiotics raze the normal complement of digestive bacteria that live in our intestines. These bacteria not only help us digest our food, they actively protect us from would-be invaders such as the bugs that cause food-poisoning (salmonella, shigella, campylobacter, et al) and colitis (Clostridium difficile, Klebsiella oxytoca, and kin). They also play less-understood roles in regulating immunity and other aspects of our physiology (including fat storage).

(Salmonella on otherwise-barren gut epithelial cells, courtesy the NIH.)

To get an ecological picture of the disruption, researchers at California's Stanford University and Cape Cod's Marine Biological Laboratory used a bacterial-DNA tagging technique to take a before- and after-antibiotic gut census, with the help of three volunteers on a five-day course of Cipro (ciprofloxacin). One of today's most widely used antibiotics, Cipro is considered relatively benign in its gut effects.

Still, by the end of the five days, the Cipro had produced wholesale changes in the abundance of about a third of the approximately 4,000 types of bacteria that had established a stable ecosystem in these three human guts.

None of the three volunteers reported any digestive problems through the brief trial--a finding the researchers took as confirmation of the general redundancy in our gut microflora. i.e. When some species get razed, others can generally pick up the slack. Moreover, the volunteers' gut "ecosystems" had more or less returned to normal by the four-week mark, though a few obscure species never reappeared or remained at abnormally low levels.

These exceptions may suggest that we need to know more about the lasting effects of antibiotics on our intestinal milieu. For example, the researchers note that increased risk of kidney stones results when the gut loses its complement of oxalate-degrading bacteria. The best known of these is Oxalobacter formigenes--a bug that's abundant in children, but which tends to disappear by adulthood (at least in the developed world). The disappearance has generally been attributed to O. formigenes' susceptibility to many commonly used antibiotics.

Here's the full study at PloS Biology.

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