Each human being plays host to some 100 trillion bacteria, of some 10,000 different types, weighing an average of 2 kilograms. And while in the past we dreamed of being free of microorganisms, today we know that aspiration was misguided.
The bacteria we co-exist with are key to processes like digestion and educating the immune system. But their role goes much further, as variations or alterations in their composition have been associated with all sorts of diseases: obesity and diabetes, allergies, certain types of cancer. Recent studies suggest that they may also be linked to infection with the Human Immunodeficiency Virus (HIV) or even to behavioral disorders like autism. This is why the microbiome, the community of microorganisms that inhabit the human body —more than 90% of which are bacteria— is now known as the forgotten organ.
Some of the top international experts in the microbiome presented and commented on the latest work in this area at B·Debate, an initiative of Biocat and the “la Caixa” Foundation to promote scientific debate.
The main conclusions of this debate are:
“We’ve known that microorganisms exist for some time now, but until recently they were contaminants. The dream was to be bacteria free,” remembered Francisco Guarner, head of the IBD Section at Vall d’Hebron University Hospital and one of the scientific leaders of this B·Debate. But when scientists managed to breed mice without germs, “they didn’t grow, had many allergies and died surprisingly easily”: microorganisms are essential to a normal life.
Since World War II, there has been a rise in the number of cases of chronic non-communicable conditions like cancer, autism and allergies. This hasn’t happened in developing countries. One possible explanation is referred to as the hygiene hypothesis: the use of antibiotics, increase in cesarean births, decrease in breastfeeding and, in general, increased asepsis in wealthy countries has limited our contact with certain microorganisms that are necessary to educate our defenses. This is why, according to Guarner, “the immune system makes more mistakes and changes to the traditional microbiome may be the origin of this increase in disease.”
But why the relatively sudden interest in the microbiome? Because of technology. “New DNA sequencing techniques have allowed us to look at and study our other genome, that of all those microorganisms,” said M. Luz Calle, director of the Bioinformatics and Medical Statistics Group at the University of Vic-Central University of Catalonia. This technology can not only identify the types of microorganisms but also the genes they contain.
In general, we have an average of 600,000 microbial genes in our gut alone and, in the words of Dusko Ehrlich, director emeritus of the French National Institute for Agricultural Research, “with regard to the microbiome as well, it’s better to be rich than poor.” The lower the diversity, the greater the tendency to accumulate fat, to develop diabetes and, in general, to be in poorer health.