How do antibiotics change microbiota when given to a newborn infant?
Antibiotics are designed to kill the bacteria that make us sick. We are increasingly aware that they also killing the bacteria that makes us healthy – the “good bacteria”. There are many consequences of this: our gut microbiota help us extract energy from food, and they regulate how much weight a baby gains. If we alter the microbiota we change the way the baby extracts energy from food, and the baby gains weight. We are seeing that this may lead to obesity later in life as well as the possible development of other diseases.
So, if the wrong microbiota is there, the baby extracts more energy from food?
Two babies eating the same amount of food might extract different amounts of energy based on their gut microbiota. We know that antibiotics can change the microbiota, so this might be one way that we find increased obesity in babies that have received antibiotics.
What is the proof of this hypothesis?
There is a lot of research still to be done, but we have emerging proof. There are more than a dozen studies that look at antibiotics and obesity, and they find an association – infants that received antibiotics are more likely to be overweight as children or teenagers. There are fewer studies on the microbiota, but we do have evidence that antibiotics change the microbiome. We see that one or two exposures early in life can have a long-term effect.
What differences do we see between infants that received antibiotics in the first six months, vs those that did not?
It depends on the population that you study - rates are different around the world - but in general we see up to a 50 percent increase in risk of obesity in those infants taking antibiotics.
How do animal models help in the studies?
In babies, we only observe, but using animals (usually mice) means we can actually deliver the antibiotics. We can deliver different types of antibiotics, as well as looking closely at the timing of the dosage, so we can study the effect of antibiotics in pregnancy and at different stages of the young animal’s life. We can also do experiments where we transplant the microbiome from an animal that has received antibiotics into a germ-free animal to see how the microbiome is causing an effect.
What do the experiments show?
The experiments in the mice show that if you give antibiotics to a young animal just after they are born, you see increased inflammation and increased fat mass. This is especially true if you put the mouse on a high fat diet. We believe this mimics what is happening in developed countries, where we are using more antibiotics than we used to in the past, coupled with a higher fat diet in general. We are also seeing insulin resistance, which is an early sign of diabetes.
So, what is the message to pediatricians? Think twice before prescribing antibiotics to infants?
We know that there are scenarios where we need antibiotics – they can be life-saving when they are really needed. Some studies have shown, however, that up to 30 percent of antibiotic prescriptions are not necessary, for example in the case of a viral infection where the drug will not aid recovery. We know that the message is getting through. A study in Canada in 1995 found that two out of every three babies was receiving antibiotics before they turned one year old. The study was repeated in 2010, and it had gone down to one in three babies receiving antibiotics before turning one. So, there is some progress.