Evolving Clostridium difficile Germs Spreading in Hospitals

A new study reveals that Clostridium difficile, a bacterium that causes debilitating diarrhea, is evolving into two separate species, with one group highly adapted to spread in hospitals.

Researchers at the Wellcome Sanger Institute (Hinxton, United Kingdom), the London School of Hygiene & Tropical Medicine (LSHTM; United Kingdom), and other institutions undertook a large-scale genomic analysis of 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 analyzing all the genomes, the researchers discovered that classical C. difficile is currently evolving into another, separate species.

The emerging species, C. difficile clade A, made up approximately 70% of the samples from hospital patients. Clade A had changes in genes that metabolize simple sugars, as well as in the genes involved in forming spores, giving it much greater resistance to hospital disinfectants. Further analysis revealed that while Clade A first appeared about 76,000 years ago, the number of different strains started to increase at the end of the 16th Century, before the founding of modern hospitals. This group has since thrived in hospital settings, with many strains that keep adapting and evolving. The study was published on August 12, 2019, in Nature Genetics.

“Our study provides genome and laboratory based evidence that human lifestyles can drive bacteria to form new species so they can spread more effectively,” said senior Trevor Lawley, PhD, of the Wellcome Sanger Institute. “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 bacterium.”

“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,” said lead author Nitin Kumar, PhD, of the Wellcome Sanger Institute. “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.”

C. difficile exists in the environment as a dormant spore. To colonize the gut, the spores need to germinate and turn in active, toxin-producing bacteria. Antibiotics that alter the gastrointestinal microbiota facilitate this germination, allowing C. difficile infection, a significant public health problem.

Related Links:
Wellcome Sanger Institute
London School of Hygiene & Tropical Medicine