Study: Diarrhea-inducing bacteria C. diff evolves into new strain that thrives in hospitals

LONDON — The leading cause of antibiotic-associated diarrhea is evolving and adapting in response to human behaviors, diets, and cleaning methods, according to a new study. Scientists at the Wellcome Sanger Institute and the London School of Hygiene & Tropical Medicine say the gut-infecting bacteria best known as C. diff (Clostridium difficile) is evolving into two species, and one of those species is specially adapted to spread and thrive in hospitals.

Researchers say this new species of bacteria appears to have changed genetically, allowing it to thrive off of a typically Western sugar-rich diet, withstand typical hospital cleaning measures, and spread very easily. Despite the fact that scientists have just discovered this new strain, they say that it likely began emerging around 76,000 years ago, and already accounts for an estimated two-thirds of healthcare related C. difficile infections.

Researchers say that hospitals and other health care facilities should take their findings into consideration regarding cleanup and infection control procedures, as well as patient diet choices.

Experiencing a bout of diarrhea due to C. diff is very common. In fact, C. difficile is found in the gut of one in every 30 healthy adults. While it is usually kept under control by other gut bacteria, the use of antibiotics can give C. difficile an opportunity to cause bowel inflammation or moderate to severe diarrhea.

So, in an effort to better understand how C. difficile continues to adapt and evolve to human behavior, researchers collected 906 different strains of the bacteria collected from humans, dogs, pigs, horses, and the environment. After analyzing each strain’s DNA, and cross referencing genomes, researchers discovered that C. diff is evolving into two species.

“Our large-scale genetic analysis allowed us to discover that C. difficile is currently forming a new species with one group specialized to spread in hospital environments. This emerging species has existed for thousands of years, but this is the first time anyone has studied C. difficile genomes in this way to identify it. This particular bacteria was primed to take advantage of modern healthcare practices and human diets, before hospitals even existed,” explains joint first author Dr Nitin Kumar in a statement.

Classified as C. difficile clade A, this new hospital-friendly strain accounted for about 70% of hospital patient samples used in the study. Researchers noticed that the new strain exhibited changes in sugar metabolizing genomes, so they set up a diet experiment involving lab mice. They found that C. difficile clade A spread more efficiently in mice who ate a high sugar diet. Genes responsible for spore formation also evolved, giving the new strain an increased ability to resist hospital disinfectants.

“Our study provides genome and laboratory based evidence that human lifestyles can drive bacteria to form new species so they can spread more effectively. We show that strains of C. difficile bacteria have continued to evolve in response to modern diets and healthcare systems and reveal that focusing on diet and looking for new disinfectants could help in the fight against this bacteria,” comments senior author Dr. Trevor Lawley.

This was the largest ever genomic study of C. diff, and researchers say that it has provided modern science with an entirely new understanding of how bacterial evolution works.

“It reveals the importance of genomic surveillance of bacteria. Ultimately, this could help understand how other dangerous pathogens evolve by adapting to changes in human lifestyles and healthcare regimes which could then inform healthcare policies,” says author professor Brendan Wren.

The study is published in the scientific journal Nature Genetics.

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John Anderer

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