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Joyride: Brief post-antibiotic sugar spike gives pathogens a lift

candy shackLet's be clear: Antibiotics are a modern miracle. They're also ancient history: During ancient times, moldy bread was traditionally used in Greece and Serbia to treat wounds and infections. Russian peasants used warm soil to cure infected wounds. Sumerian doctors gave patients beer soup mixed with turtle shells and snake skins. Babylonian doctors healed the eyes using a mixture of frog bile and sour milk. You get the drift.

At the same time, it's not exactly breaking news that a course of antibiotics can wreak havoc with your gastrointestinal tract, where infamous intestinal pathogens such as salmonella and C. difficile can run amok.

“Antibiotics open the door for these pathogens to take hold," according to Stanford microbiologist Justin Sonnenburg, PhD.

As I wrote in my press release about some exciting recent work by Sonnenburg, a healthy person's large intestine is a menagerie teeming with miniature lifeforms:

The thousands of distinct bacterial strains that normally inhabit this challenging but nutrient-rich niche have adapted to it so well that we have difficulty living without them. They manufacture vitamins, provide critical training to our immune systems and even guide the development of our own tissues.

In return, our gut pays these industrious Oompa-Loompas salaries made of sugar - not common table sugar, but more exotic types, with names like fucose and sialic acid. Cells lining the intestine extrude long chains of such sugar varieties (these chains go by a familiar name: "mucus") to feed its one-celled workhorses - as well as to keep them at arm's length, so that they don't get into the bloodstream and cause sepsis.

Everybody's having fun until along come antibiotics and somebody gets hurt. The decimated gut-microbe ecosystem begins bouncing back within a few days, but  for as much as a month after a round of antibiotics we're at heightened risk for infection by some bad, bad bugs.

In a new study, Sonnenburg and his colleagues snared some clues about how that works. They found that antibiotics' inadvertent but inevitable gut-bugicide generates a transient surplus of sugars, including sialic acid and fucose, that have been liberated from gut mucus by good bugs who bit the dust before they got a chance to munch their lunch.

Salmonella lacks the equipment for carving sialic acid and fucose loose from the intestine's extruded mucus, but it knows how to eat them. The bonanza, Sonnenburg's team found, gives the pathogen the energy it needs to gain a toehold and launch a toxic takeover, leaving our gut in its hands.

Sonnenburg thinks there may be ways to slam the door that antibiotics open for unwanted intruders. For example, specialized probiotics with big appetites for fucose or sialic acid could be co-administered along with the antibiotics, cutting off the the nasty bugs' stash until the nice ones repopulate the gut.

Sonnenburg's work appears online in Nature.

Previously: The future of probiotics, Eat a germ, fight an allergy, What if gut-bacteria communities "remember" past antibiotic exposures? and Researchers manipulate microbes in gut
Photo by Lee Cannon

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