Antibiotics have revolutionized the treatment of infections, but are generally overused and often used against viral infections. Antibiotics are only effective against bacterial infections. Our gut microbes, essential to our health and immunity, consist mostly of bacterial populations. A study at Stanford University School of Medicine showed that a relatively benign antibiotic causes immense changes in the composition of gut microbes (bacteria). These changes are enhanced by repeated treatments. Although microbial populations recovered when treatments were stopped, the microbial composition was permanently changed after the second round of antibiotic.
Gut microbial diversity
More than a 1000 varieties of microbes inhabit our intestines. The nature and function of these diverse groups of microbes is not well understood. But when the community of intestinal microbes is disturbed by infection with a pathogenic bacteria or antibiotics, some populations overgrow the rest of the microbial community. Clostridium difficile (C. difficile), which is normally present in small amounts in the gut, is kept in check by the other members of the microbial community. When it overgrows, it causes abdominal distress, nausea, diarrhea, and can lead to death, especially in the elderly or other vulnerable individuals. Maintaining the diverse community of gut microbes is essential for absorption of nutrients, generation of vitamins and essential amino acids, breaking down toxins, and healthy immune responses.
Antibiotics alter gut microbial diversity
The researchers at Stanford analyzed stool samples from three healthy volunteers for 10 months using DNA sequencing techniques. During this time, five-day regimens of ciproflaxin were administered, six months apart. Although the volunteers suffered no gastrointestinal distress, the changes in their intestinal microbe diversity were huge. “The effect of ciproflaxin on the gut microbiota was profound and rapid,” write the researchers (Dethlefsen, L. and Relman, D.A.). It took only three to four days for the antibiotic to affect the microbial composition. About one week after the end of the antibiotic treatments, microbial populations resembled the initial composition, but not completely. About 25 to 50 percent of the microbial community before antibiotic treatment was permanently wiped out after the second round of antibiotics in all three subjects. The changed microbial composition remained stable for two months until the end of the study.
Similar results have been seen in experiments with mice, using different antibiotics. The results with ciproflaxin raise concerns about repeated rounds of antibiotics and long term antibiotic treatments. Now, we don’t just need to worry about outgrowth of drug-resistant bacteria and overgrowth of pathogenic bacteria, but also about changes in the diversity of beneficial microbes. So use antibiotics only when really needed. It is not known whether antibiotics contaminating our food supply and water produce significant changes in the microbial population. Whether probiotics can counter the changes in microbial composition caused by antibiotic treatment, needs to be studied.
Dethlefsen,L. and Relman, D.L. Incomplete recovery and individual responses of the human distal gut microbiota to repeated antibiotic perturbation. Proceedings of the National Academy of Sciences (2010) DOI:10.1073/pnas.10000087107