By disturbing our inner ecosystem, Carl Zimmer says, antibiotics can affect our health:
In some cases, for example, antibiotics can make it easier for pathogens to invade. Eric Pamer of Memorial Sloan Kettering Cancer Center and his collegues recently provided a striking demonstration of this effect. They gave mice a single dose of the antibiotic clindamycin. Ninety percent of the diversity in the gut of the mice disappeared and was still gone four weeks after the treatment. The scientists then inoculated the mice with the spores of Clostridium difficile, a particularly nasty pathogen that can cause lethal cases of diarrhea. They invariably got an overwhelming infection, and half of them died within a few days. Pamer could wait as long as ten days after giving the mice antibiotics, and they were still felled by C. difficile. Healthy mice, on the other hand, easily kept the invasion in check.
Antibiotics may also exert subtler, longer-term effects on our health. Matthew Kronman of Seattle Children’s Hospital and his colleagues, for example, recently reviewed the medical records of over a million people. They found that children who took antibiotics were at greater risk of developing inflammatory bowel disease later in life. The more antibiotics they took, the greater the risk. Similar studies have found a potential link to asthma as well.
A study carried out by Dennis Kasper at Harvard hints at how antibiotics can send the immune system off the rails. They reared mice in isolated containers so that they never developed a microbiome. The germ-free rodents developed unusually high levels of an aggressive type of immune cell called an invariant natural killer T cell. If Kasper inoculated baby germ-free mice with a normal microbiome, the T cells remained rare. Antibiotics, the scientists propose, allow the T cells to explode and to run amok.
It’s even possible that long-term antibiotic use may influence how people put on fat. Martin Blaser of New York University and his colleagues carried out an experiment on mice in which they fed the animals antibiotics and then tracked their metabolism. The scientists found that the mice fed with antibiotics developed a higher percentage of body fat than mice that didn’t.*
Antibiotics cause this rise in fat, Blaser and his colleagues argue, by creating long-term changes in the microbiome. The species fostered in the mice produce enzymes that change not just how they break down our food, but also send signals to our own hormones to change the way we store energy from our food.