Researchers were surprised to find the most diverse collection of bodily bacteria seen in humans is isolated to the tribe of Yanomami villagers that live in the Amazonian jungles of southern Venezuela.
The microbiome of people living in industrialized countries is about 40 percent less diverse, suggesting a link between modern antibiotics and diets and reduced microbiome diversity, NYU Langone Medical Center reported.
Yanomami villagers remained isolated from the rest of society until 2009, when they were contacted by a medical expedition. They have been living as hunter-gatherers for hundreds of generations. A team of researchers gained valuable insight into their unusually diverse microbiomes by looking at oral and fecal samples.
"Our results bolster a growing body of data suggesting a link between, on the one hand, decreased bacterial diversity, industrialized diets, and modern antibiotics, and on the other, immunological and metabolic diseases--such as obesity, asthma, allergies, and diabetes, which have dramatically increased since the 1970s. We believe there is something environmental occurring in the past 30 years that is driving these diseases. We think the microbiome could be involved," said Maria Dominguez-Bello, associate professor of medicine at NYU Langone Medical Center and the senior author of the study.
The researchers analyzed bacterial samples from 34 Yanomami villagers, consisting of 28 skin and oral samples and 11 fecal samples.This bacterial DNA was compared with samples from populations in the U.S., the Amazonian Guahibo Amerindians in Venezuela, and residents of rural Malawian communities in southeast Africa. The last two tribal populations have more exposure to western culture than the Yanomami villagers.
"There is a gradient of diversity in feces and skin that is inversely proportional to exposure to antibiotics and processed foods," said co-author Jose Clemente, assistant professor of genetics and genomics at the Icahn School of Medicine at Mount Sinai. "Even minimal exposure greatly decreases diversity and removes potentially beneficial bacteria from our microbiome."
The team did not find a single dominant taxonomic group of bacteria in the Yanomami skin samples, but the U.S. samples had lower diversity and a high prevalence of Staphylococcus, Corynebacterium, Neisseriaceae, and Propionibacterium. The gut and oral bacteria of the Yanomami villagers contained genes coding for antibiotic resistance, most likely linked to natural antibiotics found in soil. The researchers were also surprised to find traces of resistance to synthetic antibiotics.
"During the 1940s and 1950s, in the heyday of pharmaceutical antibiotic development, most antibiotics were derived from naturally occurring bacteria in the soil," said co-author Gautam Dantas, associate professor of pathology, immunology, and biomedical engineering at Washington University School of Medicine. "So, we would expect that natural resistance to antibiotics would emerge over millions of years of evolution. We didn't expect to find resistance to modern synthetic antibiotics."
The resistance genes appeared to be silenced because cultural strains of the bacteria were sensitive to antibiotics, suggesting exposure to antibiotics is not necessary to produce antibiotic-resistant genes. These findings could help explain the impressive rate at which bacteria develop resistance to newly-developed antibiotics used in industrialized cultures.
The findings were published in a recent edition of the journal Science Advances.
