OUR MICROBIAL VOYAGE
Our relationship with microbes begins at birth. Infants passing through their mother’s vagina pick up their first microbial passengers when they are coated with founder bacteria such as Lactobacillus johnsonii.
Then, breast milk delivers more bacteria along with complex carbohydrates that act like fertilizer, enabling beneficial organisms to take hold in infants’ guts.
The microbial pile-on continues as babies are passed around to friends and family, each with their own unique community of bacteria and fungi on their skin and in their mouths. It accelerates as babies start crawling around, gumming their toys and petting the family dog and cat.
By age five, children have amassed trillions of bacteria, fungi and viruses — collectively known as the microbiota or microbiome. The invisible organisms have taken up residence on their skin, and in their mouths, lungs and guts.
The microbiota is so rich that scientists estimate that for every human cell in the body, there are 10 microbes.
They are found from head to toe, but the gut is home to most of them.
One gram of feces is populated with more microbes than all the people on Earth, researcher Brett Finlay at the University of British Columbia likes to point out.
Add all the organisms up and they can weigh almost as much as the liver. And scientists say they are just as important.
The microbes help digest food and synthesize key nutrients such as vitamins B and K. They keep pathogens at bay. Their secretions moisturize the skin. The organisms also interact with their human hosts, stimulating healthy development of the immune system. And they pump out signalling molecules that scientists now suspect affect everything from brain development to weight gain.
The estimated 100 trillion microbes in and on the average human belong to as many as 1,000 different types or strains. The collection is more diverse in people who live with animals and eat an unrefined diet with plenty of vegetables.
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