Many bacteria living in the large intestine alter primary bile acid into secondary bile acid. Since antibiotics kill off bile-altering bacteria, this may be why antibiotics increase the risk for C. difficile infection. Primary bile acids are made from cholesterol in the liver and make their way to the intestines. Bacteria in the large intestine convert them into secondary bile acids such as deoxycholate. Bile acids form micelles to help digest and absorb fats. They also help metabolize glucose, lipoproteins, and some drugs.
The researchers found that primary bile acids (found in the small intestine) allowed the growth of C. difficile, but secondary bile acids (produced by bacteria in the large intestine) inhibited C. difficile growth. When they treated mice with various antibiotics - cefoperazone, clindamycin, or vancomycin - the levels of secondary bile acids such as deoxycholate and lithocholate dropped, allowing C. difficile to grow.
“These findings are a first step in understanding how the gut microbiota regulates bile acids throughout the intestine … hopefully they will aid the development of future therapies for C. difficile infection and other metabolically relevant disorders such as obesity and diabetes” says Theriot.
Sources: mSphere, Science Daily, Wikipedia