Fascinating discoveries about the normal bacterial inhabitants of our human bodies - our microbiome - now appear in leading medical research journals nearly every week. This field of study has become one of the fastest-moving and most dramatic areas of scientific progress in decades.

Fascinating discoveries about the normal bacterial inhabitants of our human bodies � our microbiome � now appear in leading medical research journals nearly every week.

This field of study has become one of the fastest-moving and most dramatic areas of scientific progress in decades.

Just when one thinks the field has peaked, newly published research findings provide a fundamentally important, new health insight related to the microbiome. A recent report from collaborating scientists in Pittsburgh and Philadelphia emphasizes this very fact.

While developing in the womb, babies are sterile, or nearly so. As they enter the world through the messy circumstances of a typical birth, bacteria rapidly accumulate on their skin and in their intestinal tract. Soon, we are carrying trillions of these bacteria with us, and we will do so for the remainder of our lives. Our microbiome becomes a huge part of our health and well-being.

The Pennsylvania scientists made a very important observation during experiments on the intestinal microbiome of newborn mice. They found that mice treated with antibiotics soon after birth develop an altered intestinal microbiome. Bacteria numbers in the intestines are reduced, and the types of bacteria are changed.

They also noticed reduced numbers of infection-fighting white blood cells in the bloodstream. This unexpected finding became a main focus of their work.

The researchers went on to identify with great precision the molecular pathways that link bacteria in the intestines to white-blood-cell formation, which occurs in the bone marrow. And they further solidified the significance of their findings by showing that the antibiotic-treated mice with low numbers of infection-fighting white blood cells were susceptible to serious infection.

These findings in mice probably explain some of what we have long known about newborn human infants but has heretofore been unexplained. For example, we know that white-blood-cell numbers are naturally high in babies in the first few days of life. It now seems this is explained by accumulating numbers of bacteria in the intestines.

We also know that early exposure to antibiotics in human newborns increases the risk of serious infection in the weeks ahead. It now seems this is caused by an altered microbiome, which in turn causes a reduction in infection-fighting white blood cells, limiting the immune system�s ability to fight infection in vulnerable newborns.

As a pediatrician and a scientist, I have been fascinated by normal human development for many years. But I must admit that I am truly astounded by the explosion of new knowledge about the microbiome and its effects on our immune system and fundamental aspects of our physiology.

Because of microbiome research, it seems to me we are rapidly defining new principles of human health. These are especially applicable in newborns, when the microbiome is first developing and babies are susceptible to a host of infections and diseases.

As we learn more, we will be able to convert our newly gained knowledge into new preventive measures and innovative treatments. I have a strong feeling that paradigm-changing discoveries are in store for many years ahead.

Dr. John Barnard is president of the Research Institute at Nationwide Children's Hospital.

john.barnard@nationwidechildrens.org