Diarrhoea-causing bacteria adapted to spread in hospitals

Scientists have discovered that the gut-infecting bacterium Clostridium difficile is evolving into two separate species, with one group highly adapted to spread in hospitals.

Researchers at the Wellcome Sanger Institute, Hudson Institute of Medical Research, London School of Hygiene and Tropical Medicine and collaborators, identified genetic changes in the newly-emerging species that allow it to thrive on the Western sugar-rich diet, evade common hospital disinfectants and spread easily. The researchers estimate this emerging species, which can cause debilitating diarrhoea, started to appear thousands of years ago and accounts for over two thirds of healthcare C. difficile infections.

Dr Sam Forster

Published in Nature Genetics, the largest ever genomic study of C. difficile shows how bacteria can evolve into a new species and demonstrates that C. difficile is continuing to evolve in response to human behaviour. The results could help inform patient diet and infection control in hospitals.

C. difficile bacteria can infect the gut and are the leading cause of antibiotic-associated diarrhoea worldwide*. In a healthy person who is not taking antibiotics, millions of ‘good’ bacteria in the gut keep the C. difficile under control. However, antibiotics wipe out the normal gut bacteria, leaving the patient vulnerable to C. difficile infection in the gut. This is then difficult to treat and can cause bowel inflammation and severe diarrhoea.

Often found in hospital environments, C. difficile forms resistant spores that allow it to remain on surfaces and spread easily between people, making it a significant burden on the healthcare system. To understand how this bacterium is evolving, researchers collected and cultured 906 strains of C. difficile isolated from humans, animals, such as dogs, pigs and horses, and the environment. By sequencing the DNA of each strain, and comparing and analysing all the genomes, the researchers discovered that C. difficile is currently evolving into two separate species.

Leading bacterial genomics expert and paper author, Dr Sam Forster from Hudson Institute said “This work provides a new perspective into C. difficile outbreaks and how they could be managed, especially in environments such as hospitals and aged care facilities. The study demonstrates how detailed genomic understanding from fundamental research can provide important insights into the way our behaviour shapes the disease-causing bacteria we encounter.”

Dr Nitin Kumar, joint first author from the Wellcome Sanger Institute, said “Our large-scale genetic analysis allowed us to discover that C. difficile is currently forming a new species with one group specialised 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.”

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