Gut-infecting bacterium Clostridium difficile is evolving
into two separate species, with one group highly adapted to spread in hospitals
The Wellcome Sanger Institute – August 12,
2019 -- 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, London
School of Hygiene & 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. Able to
cause debilitating diarrhea, they estimated this emerging species started to
appear thousands of years ago, and accounts for over two thirds of healthcare
C. difficile infections.
Published in Nature Genetics today (12
August), 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*. While
someone is healthy and 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 diarrhea.
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.
“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.”
--Dr Nitin Kumar, joint first
author from the Wellcome Sanger Institute
The researchers found that this emerging
species, named C. difficile clade A, made up approximately 70 per cent of the
samples from hospital patients. It had changes in genes that metabolise simple
sugars, so the researchers then studied C. difficile in mice**, and found that
the newly emerging strains colonised mice better when their diet was enriched
with sugar. It had also evolved
differences in the genes involved in forming spores, giving much greater
resistance to common hospital disinfectants. These changes allow it to spread
more easily in healthcare environments.
Dating analysis revealed that while C.
difficile Clade A first appeared about 76,000 years ago, the number of
different strains of this 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.
“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.”
--Dr Trevor Lawley, the senior
author from the Wellcome Sanger Institute
“This largest ever collection and analysis of C.
difficile whole genomes, from 33 countries worldwide, gives us a whole new
understanding of bacterial evolution. 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.”
--Prof Brendan Wren, an author
from the London School of Hygiene &
Tropical Medicine
No comments:
Post a Comment