The strange science of breast milk may change the way you think about bacteria.
Jenny Nicholls on the 39 trillion, mostly wondrous, microbial cells living in and on us.
It was either the club sandwiches (office shout), or the takeaway chicken foo yung I ate later. By the next day, I was vomiting, twice an hour, every hour.
After 48 hours of nonstop clenching, my stomach felt like an orange on a motorway, and I was barfing (sensitive readers, turn away) blood. So I caught a cab to the doctor’s, a bowl on my knees. Even though the trip lasted only a few minutes, I didn’t make it out of the cab without vomiting. At the doc’s, I was ushered into a side room where I could throw up in private.
My boyfriend, a med student, gleefully diagnosed salmonella poisoning, and prescribed gallons of water to keep me hydrated. My GP, who gave me an anti- emetic shot, agreed. Although I was better in a few days, my stomach felt raw for weeks.
Although this brush with “pathogenic” (disease-causing) bacteria was decades ago, I remember it vividly. The residents of Havelock North, I have no doubt, will recall the frightening campylobacter bacteria contamination of their public water supply for the rest of their lives.
For such tiny animals, bacteria cast a long shadow. Yersinia pestis, the plague bacterium (aka the Black Death) mowed down so many it changed the course of history – and Mycobacterium tuberculosi (aka “consumption”) killed even more, choking to death the Brontës, Chekhov, Kafka, Keats, D.H. Lawrence, Katherine Mansfield, Molière, George Orwell and Chopin, among millions of others.
The “lingering cultural scar” of these bugs, as award-winning science writer Ed Yong puts it in his astounding new book I Contain Multitudes (Bodley Head, $55), casts bacteria as feared contaminants. Germs are not only bad, they are disgusting. Exterminate!
But this widely held view is not only wrong, it is wrong on an epic scale, explains Yong (interviewed, overleaf ). Most microbes are not pathogens. Fewer than 100 species of bacteria cause illness in humans.
It is hard to get your head around,
but the 30 trillion cells in your body are accompanied by an estimated 39 trillion microbial ones. This is your microbiome and it behaves, Yong explains, like an organ, “as important as a stomach or an eye”.
So, what is your microbiome made up of? Bacteria, mostly – but there are also fungi, mysterious organisms called archaea, and vast numbers of viruses, mostly infecting the bacteria. It’s a jungle in there – and also a desert and a forest and a city. Our body, inside and out, contains a range of environments, each home to its own fauna.
“Each of us has our own distinctive microbiome,” writes Yong, “sculpted by the genes we inherited, the places we’ve lived in, the drugs we’ve taken, the food we’ve eaten, the years we’ve lived, the hands we’ve shaken.”
Your cells carry around 20,000 genes, but the microbes inside you contain 500 times more – functioning, in other words, like tiny, independent chemical factories. “This genetic wealth, combined with their rapid evolution, makes them masters of biochemistry, able to adapt to any possible challenge. They help to digest our food, releasing otherwise inaccessible nutrients. They produce vitamins and minerals that are missing from our diet. They break down toxins and hazardous chemicals. They (even) protect us from disease.”
It now seems our body wouldn’t develop properly without a balance of microbes, and a long list of complaints have been linked to disruptions in the biodiversity of our germs. A disease like cholera, for example, could be likened to an environmental disaster, such as the one in Guam, where introduced tree snakes have swallowed whole species of native birds.
One day, we might well be able to tweak our microbiomes to fix diseases as diverse as allergies, diabetes, depression and heart disease. And not just ours. Yong also explores the idea of a building’s microbiome – like that of a hospital, where fresh air can bring in harmless outdoor microbes and whisk away pathogens emitted by patients.
Emitted? “All of us are constantly seeding the world with our microbes,” he writes. “Every time we walk, talk, scratch, shuffle or sneeze, we cast a personalised cloud of microbes into space. Every person aerosolises around 37 million bacteria per hour.”
So Florence Nightingale was ahead of her time when she put patients next to open windows. Yong quotes a researcher who found hospital air, to her shock, to be a bouillabaisse of pathogens rare or absent in the air just outside.
Although he doesn’t over-hype the science, Yong conveys the excitement of evolving discoveries in a field that’s hotter than hot. (Bugs. Fashionable. Yep.)
Another spectacular finding involves human breast milk, now known to contain a ridiculously long list of complex sugars; more than 200 different kinds. This is odd, because human babies cannot digest them.
But something else can. It seems they don’t feed the baby at all – but the baby’s bacteria. Eek!
Bifidobacterium infantis, in particular, thrives on this diet, which makes it the dominant bacteria in the guts of breastfed babies. And the bug is a stellar tenant, helping to “calibrate” the baby’s immune system – which is, by the way, not so much “immature” as dialled back, to allow an influx of bacteria it needs.
“The obvious message is that breast milk is good,” said Yong in an interview with Vox magazine. “But if you’re not breastfeeding, you’re not screwing up your baby’s microbiome. One of the things I noticed when I was researching the book is that these pathways are very resilient. The development of the microbiome can go down lots of different paths.”
Breast milk is just one example of the mind-boggling symbiosis between bacteria and their hosts, the true extent of which we are only just beginning to understand. +
“Every time we walk, talk, scratch, shuffle or sneeze, we cast a personalised cloud of microbes into space.”