Superbugs or antibiotic-resistant bacteria may have originated from the microbes that existed 450-million-years-ago and well before the age of dinosaurs, according to scientists. At that time, the animals first crawled onto land.
A new study has highlighted the evolutionary history of enterococci, pathogens which evolved nearly indestructible properties. This has now become a leading cause of modern antibiotic-resistant infections in hospitals.
Today, a leading public health concern worldwide is the antibiotic resistance. Some microbes, often referred to as “superbugs,” are resistant to virtually all antibiotics.
“By analysing the genomes and behaviours of today’s enterococci, we were able to rewind the clock back to their earliest existence and piece together a picture of how these organisms were shaped into what they are today” said Ashlee M Earl, from the Broad Institute of MIT and Harvard.“Understanding how the environment in which microbes live leads to new properties could help us to predict how microbes will adapt to the use of antibiotics, antimicrobial hand soaps, disinfectants and other products intended to control their spread,” said Earl.
The picture the researchers pieced together begins with the dawn of life. Bacteria arose nearly four billion years ago, and the planet has teemed with them ever since, including the sea.
Animals first arose in the sea during the time known as the Cambrian Explosion, 542 million years ago. As animals emerged in a sea of bacteria, bacteria learnt to live in and on them.
The researchers found that all species of enterococci, including those that have never been found in hospitals, were naturally resistant to dryness, starvation, disinfectants and many antibiotics.
Since enterococci live in the intestines of most land animals, it is likely that they were also in the intestines of ones that are now extinct, including dinosaurs and the first millipede-like organisms to crawl onto land.
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Comparison of the genomes of these bacteria provided evidence that this was indeed the case. Researchers also found that new species of enterococci appeared whenever new types of animals appeared.
Sea animals excrete intestinal microbes into the ocean, which usually contains about 5,000 mostly harmless bacteria per drop of water.They sink to the seafloor into microbe-rich sediments, and are consumed by worms, shellfish and other sea scavengers.
Those are then eaten by fish, and the microbes continue to circulate throughout the food chain. However, on land, intestinal microbes are excreted as feces, where they often dry out and most die over time. However enterococci are unusually hardy and can withstand drying out and starvation.
“We now know what genes were gained by enterococci hundreds of millions of years ago, when they became resistant to drying out, and to disinfectants and antibiotics that attack their cell walls,” said Michael S Gilmore, from the Harvard Infectious Disease Institute in the US.
The research was published in the journal Cell.
(With inputs from PTI)