A new study has revealed that antibiotics have an impact, which is broader and more complex than previously known, on the microorganisms that live in an animal's gut.

The research at Oregon State University helps explain in much more detail why antibiotics can have unwanted side effects, especially in disrupting the natural and beneficial microbiota of the gastrointestinal system, and also suggests that powerful, long-term antibiotic use can have even more far-reaching effects.

Scientists now suspect that antibiotic use, and especially overuse, can have unwanted effects on everything from the immune system to glucose metabolism, food absorption, obesity, stress and behavior.

The issues are rising in importance, since 40 percent of all adults and 70 percent of all children take one or more antibiotics every year, not to mention their use in billions of food animals. Although when used properly antibiotics can help treat life-threatening bacterial infections, more than 10 percent of people who receive the medications can suffer from adverse side effects.

Researcher Andrey Morgun said that prior to this most people thought antibiotics only depleted microbiota and diminished several important immune functions that take place in the gut, which actually is only about one-third of the picture.

Morgun added that they also kill intestinal epithelium and destruction of the intestinal epithelium is important because this is the site of nutrient absorption, part of our immune system and it has other biological functions that play a role in human health.

The research also found that antibiotics and antibiotic-resistant microbes caused significant changes in mitochondrial function, which in turn can lead to more epithelial cell death.

Morgun concluded that when the host microbe communication system gets out of balance it can lead to a chain of seemingly unrelated problems.

The work is published online in the journal Gut.