Thursday, January 26, 2023

A major study uncovers the transfer of germs with close people: Up to a third of bacteria in the mouth

There is one troubling fact: there are more bacterial cells (38 trillion) in a person’s body than human cells (30 trillion). One of the priests of microbiology, the American Frederick Bushman, even invites us to stop viewing the human being as an individual organism and to consider it as a coral reef inhabited by billions of other creatures. A macro-study now shows that these tiny tenants jump from person to person in enormous proportions: Two cohabitants share up to 12% of stress in their intestines and up to 32% in their mouths, with risk factors such as cancer, obesity, and obesity. The bacteria associated with it are also included. , diabetes and heart disease, according to the first author of the research, Spanish microbiologist Miria Valles. Some diseases historically considered non-communicable have an infectious component. “This is a paradigm shift”, declares Wallace.

The new study analyzed stool and saliva samples from nearly 5,000 people from 20 countries on five continents. The results confirm that social interactions determine the composition of the so-called microbiome in the gut as well. A mother shares 34% of the bacterial strains in her gut with her young children. two people living together, 12%. Two twin brothers living in separate homes, 8%. And two independent adults from the same city also 8%. Inherited microbes are lost after childbirth: this coexistence is what characterizes the microbiome. “The percentage an adult shares with his or her mother is about the same as the number of people he or she lives with or work colleagues,” says Valles of the University of Trento in Italy.

Three out of every four deaths in the world are due to so-called non-communicable diseases, such as cancer, heart attacks, strokes, diabetes and asthma. According to the World Health Organization, more than 40 million people die every year in the world from these causes. Canadian microbiologist Brett Finley introduced an intriguing hypothesis three years ago. “Are Noncommunicable Diseases Communicable?”, asked the journal Science, Finlay argued that factors such as junk food, smoking and alcohol consumption lead to imbalances in the microbiome, which may affect non-communicable diseases or their risk factors, such as obesity. According to Finlay, that altered microbiome “can be transmitted from person to person, potentially contributing to the spread of disease”.

800 species of bacteria

The new work is pointing in that direction. “Our results strengthen the hypothesis that many diseases and conditions currently considered non-communicable should be re-evaluated,” the authors said in their study published Wednesday in the journal Nature. Nature, Vanguard of the best world science. This is the largest investigation into the transmission of the human microbiome conducted to date.

The signatories looked at more than 800 species of bacteria, identifying ultra-specific strains of each. “Sharing 8% is a lot, because with those with whom we are not in contact, we have zero,” stresses Vallés, who was born in Vic (Barcelona), 32 years ago. Their study confirms that the microbiome in the mouth circulates differently than in the depths of the digestive tract. “From the oral route, the vehicle is saliva, but we still do not know the specific mechanism of the gut. This could be due to a lack of hygiene, due to a fecal-oral transmission that then reaches the gut, but it is not clear No, ”the microbiologists admit.

Color image of ‘Helicobacter pylori’ bacteria under a microscope.

Researchers from a dozen countries have participated in the macro-study, including agronomist María Carmen Collado from CSIC’s Institute of Agricultural Chemistry and Food Technology in Paterna (Valencia). Collado is an expert on the so-called vertical transmission of the microbiome, from mothers to children. “We have now seen that horizontal transmission, from person to person, is very important, much more so than was initially thought,” he highlighted.

The microbiome is in the limelight of the scientific community. Three months ago, a team from Yale University (USA) announced that a common microbe in the human gut is suspected to play a key role in the development of colorectal cancer, the world’s second deadliest tumor. Some strains of this bacterium are called morganella morgani, produce molecules that are toxic to human DNA, which cause tumors when injected into mice. Another common bacteria in the gut, the Helicobacter pyloriAssociated with an increased risk of gastric cancer.

Miria Valles’ team has identified some microbes that are more likely to circulate than others. According to the scientist, despite their obvious importance, many of them do not yet have a name. “What surprises us in general is that there are some bacteria that we know very little about, that have never been cultured, and that are on top of the world. grade [de microbios compartidos]”, warns Wallace. His group has turned to metagenomics, the large-scale analysis of all the genetic material present in stool and saliva samples.

Microbiologist Brett Finlay, pioneer of the hypothesis, applauds the new research, which he is not involved in. “This is a fascinating study, which builds on what I’ve picked up myself: that non-communicable diseases are potentially transmitted through the microbiome,” says this researcher from the University of British Columbia in Canada. “These results really reinforce the concept that you can potentially pick up bad microbes [causantes de enfermedades] From other people in a transferable way. This forces us to rethink policies against non-communicable diseases, which currently account for the largest share of morbidity and mortality worldwide,” argues Finlay. “Choose your partners well,” he jokes.

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