Study reveals how C. difficile disrupts the gut
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Last updated: Mon 23 Feb 2015 at 3am PST
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C. diff rapidly took over the guts of antibiotic-treated mice.
Image credit: University of Michigan Medical School
Infection with C. diff can result in mild to severe symptoms, such as diarrhea, fever and stomach pains. It can also lead to life-threatening conditions such as the bowel being unable to expel gas and stool due to inflammation and swelling.
While we know most cases of this major public health threat arise following antibiotic treatment, we know little about the stages and biological processes that allow C. diff to rapidly colonize the disturbed ecosystem of the gut.
Now, a new study from the University of Michigan in Ann Arbor - published in the journal Infection and Immunity - describes how it took only 24 hours for the pathogen to germinate and establish itself along the whole of the digestive tract of mice newly treated with antibiotics.
The researchers hope their findings will spur better ways of preventing and treating C. diff infections.
C. diff was producing toxin at other end of gut in 24 hours
For their study, the team introduced C. diff spores into the mouths of mice freshly treated with antibiotics - the same route through which the pathogen likely enters human patients in a care setting.They then took samples from different parts of the gut of infected mice every few hours and inspected them in special oxygen-free chambers to measure the amount and types of C. diff in each one.
The analysis showed it took only about 24 hours for the spores to develop into toxin-producing, diarrhea-inducing cells in the large intestine - at the other end of the digestive tract.
The researchers also found that the bile acids in the mice's gut activated the dormant C. diff spores, causing them to germinate and grow into cells that colonized the small intestine within 24 hours of entering the digestive tract via the mouth.
The samples also showed that C. diff was forming spores again - thus completing its life cycle - in the large intestine, from where it could be expelled in feces and infect a new host.
The team used a specially developed strain of mice for the study and a common antibiotic in the cephalosporin class. The strain of C. diff they gave the mice originated from a human patient years ago, but it can also be bought in lab- culture form.
First author Dr. Mark Koenigsknecht says:
"We introduced 100 spores through the mouth, and within 6 hours we could find 1,000 cells in the intestinal tract. We chose this strain of C. difficile because of its rapid ability to cause disease in animals, but we didn't think it would happen that quickly."
C. diff DNA was the most dominant in gut in 36 hours
The team also carried out a DNA analysis to see what had happened to the gut microbiome in the mice. By comparing mice that had been treated with antibiotics with those that had not, they found the antibiotics disrupted the bacterial colonies in the small intestine, and C. diff DNA was the most dominant within 36 hours.When they examined intestinal tissue under a microscope, the researchers found the toxin from C. diff had caused the cells lining the gut to become leaky, which in turn summoned immune cells and led to diarrhea. These changes were evident in the large intestine about 30 hours after the mice were given the C. diff spores.
The team notes that this is the first study to find evidence of toxin production and newly produced C. diff spores that can survive outside the body at the same time in a living animal.
They suggest this shows the two processes are linked and probably triggered by the same signal in the body.
Dr. Koenigsknecht is now keen to discover what that signal is, whether different strains of C. diff produce the same results, and what types of patient are most vulnerable to their effects. He notes:
"Now that we understand what C. difficile is doing, we can also go and ask more questions about how the machinery inside the cell is turning on. We have to know how to study it before we can cure it."Some of the questions the team wants to explore include finding out exactly how C. diff takes over a gut freshly decimated by antibiotics: does it prevent the growth of other bacteria? Or does it outcompete them by devouring their resources faster? And how does the pathogen communicate - if at all - with the cells of the gut lining? The researchers want to find out as much as they can about the way friendly and unfriendly bacteria communicate with the gut.
Grants from the National Institutes of Health funded the study.
Meanwhile, Medical News Today recently reported on the growing interest in transplanting fecal matter from a healthy donor as a way to treat C. diff infection. One reason for the growing interest in this type of bacteriotherapy is that unlike antibiotics, it does not wipe out the natural bacteria in the gut.
Written by Catharine Paddock PhD
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