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Further reasons to be cautious of using antibiotics, and more support for finding beneficial bacteria and other microbes to outcompete the "bad" microbes. I especially liked the last paragraph that stressed for a healthy microbiota (microbial community):"Instead of trying to kill the "bad" bacteria causing an illness, a healthy and functioning microbiota may be able to outcompete the unwanted microbes and improve immune function." From Medical Xpress:

Unwanted impact of antibiotics broader, more complex than previously known

Researchers at Oregon State University have discovered that antibiotics have an impact on the microorganisms that live in an animal's gut that's more broad and complex than previously known. The findings help to better explain some of the damage these medications can do, and set the stage for new ways to study and offset those impacts.

Researchers have known for some time that antibiotics can have unwanted side effects, especially in disrupting the natural and beneficial microbiota of the gastrointestinal system. But the new study helps explain in much more detail why that is happening, 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.

This research used a "cocktail" of four antibiotics frequently given to laboratory animals, and studied the impacts."Prior to this most people thought antibiotics only depleted microbiota and diminished several important immune functions that take place in the gut," Morgun said. "Actually that's only about one-third of the picture. They also kill intestinal epithelium. 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....Mitochondria plays a major role in cell signaling, growth and energy production, and for good health they need to function properly.

Morgun and Schulzhenko's research group also found that one of the genes affected by antibiotic treatment is critical to the communication between the host and microbe. "When the host microbe communication system gets out of balance it can lead to a chain of seemingly unrelated problems," Morgun said. Digestive dysfunction is near the top of the list, with antibiotic use linked to such issues as diarrhea and ulcerative colitis. But new research is also finding links to obesity, food absorption, depression, immune function, sepsis, allergies and asthma.

Healthy microbiota may also be another way to address growing problems with antibiotic resistance, Morgun said. Instead of trying to kill the "bad" bacteria causing an illness, a healthy and functioning microbiota may be able to outcompete the unwanted microbes and improve immune function.

Another benefit to exercising - more microbial diversity. From Medscape:

Exercise Linked to More Diverse Intestinal Microbiome

Professional athletes are big winners when it comes to their gut microflora, suggesting a beneficial effect of exercise on gastrointestinal health, investigators report in an article published online June 9 in Gut.

DNA sequencing of fecal samples from players in an international rugby union team showed considerably greater diversity of gut bacteria than samples from people who are more sedentary.

Having a gut populated with myriad species of bacteria is thought by nutritionists and gastroenterologic researchers to be a sign of good health. Conversely, the guts of obese people have consistently been found to contain fewer species of bacteria, note Siobhan F. Clarke, PhD, from the Teagasc Food Research Centre, Moorepark, Fermoy. "Our findings show that a combination of exercise and diet impacts on gut microbial diversity. In particular, the enhanced diversity of the microbiota correlates with exercise and dietary protein consumption in the athlete group," the authors write.

The investigators used 16S ribosomal RNA amplicon sequencing to evaluate stool and blood samples from 40 male elite professional rugby players (mean age, 29 years) and 46 healthy age-matched control participants. 

Relative to control participants with a high BMI, athletes and control participants with a low BMI had improved metabolic markers. In addition, although athletes had significantly increased levels of creatine kinase, they also had overall lower levels of inflammatory markers than either of the control groups.

Athletes were also found to have more diverse gut microbiota than controls, with organisms in approximately 22 different phyla, 68 families, and 113 genera. Participants with a low BMI were colonized by organisms in just 11 phyla, 33 families, and 65 genera, and participants with a high BMI had even fewer organisms in only 9 phyla, 33 families, and 61 genera.

The professional rugby players, as the investigators expected, had significantly higher levels of total energy intake than the control participants, with protein accounting for 22% of their total intake compared with 16% for control participants with a low BMI and 15% for control participants with a high BMI. When the authors looked for correlations between health parameters and diet with various microbes or microbial diversity, they found significant positive association between microbial diversity and protein intake, creatine kinase levels, and urea.