Repeated use of antibiotics alter beneficial germs

? Antibiotics can temporarily upset your stomach, but now it turns out that repeatedly taking them can trigger long-lasting changes in all those good germs that live in your gut, raising questions about lingering ill effects.

Nobody yet knows whether that leads to later health problems. But the finding is the latest in a flurry of research raising questions about how the customized bacterial zoo that thrives in our intestines forms — and whether the wrong type or amount plays a role in ailments from obesity to inflammatory bowel disease to asthma.

Don’t be grossed out: This is a story in part about, well, poop. Three healthy adults collected weeks of stool samples so that scientists could count exactly how two separate rounds of a fairly mild antibiotic caused a surprising population shift in their microbial netherworld — as some original families of germs plummeted and other types moved in to fill the gap.

It’s also a story of how we coexist with trillions of bacteria, fungi and other microbes in the skin, the nose, the digestive tract, what scientists call the human microbiome. Many are beneficial, even indispensable, especially the gut bacteria that play an underappreciated role in overall health.

“Gut communities are fundamentally important in the development of our immune system,” explains Dr. David Relman of Stanford University, who led the antibiotic study published Monday in Proceedings of the National Academy of Sciences. “Let’s not take them for granted.”

Next, Relman plans to track if antibiotics during the first or two year of life, when youngsters form what will become their unique set of gut bacteria, seem to predispose children to later immune-related diseases.

Antibiotics already should be used cautiously because they can spur infection-causing bacteria to become drug-resistant. The new research raises different questions about effects on beneficial bacteria — and if abnormalities in the microbiome really are linked to health problems, how those changes might begin.

Everyone is born with an essentially sterile digestive tract, but within days the gut is overrun with bacteria from mom and dad, the environment, first foods. Ultimately, a healthy person’s intestinal tract teems with hundreds of species of microbes, the body’s biggest concentration, with many involved in such things as digestion and immune reaction.

In the not-so-healthy, scientists have discovered that overweight people harbor different types and amounts of gut bacteria than lean people, and that losing weight can change that bacterial makeup. They’ve also found links to other digestive diseases, precancerous colon polyps — and even are pursuing a theory that early use of antibiotics disrupts the developing microbiome in ways that spur autoimmune disorders like asthma or allergies.

Of course, antibiotics aren’t the only means of disrupting our natural flora. Other research recently found that babies born by cesarean harbor quite different first bacteria than babies born vaginally, offering a possible explanation for why C-section babies are at higher risk for some infections. Likewise, the gut bacteria of premature infants contains more hospital-style germs than a full-term baby’s.