The principal theory for why the outbreak occurred was the use of fluoroquinolones, such as Ciprofloxacin, which was identified as the biggest risk factor for development of infection. Up until this time it was conventional practice for hospitals with a known problem with C. difficile to switch from using lots of Cefuroxime (previously identified as a risk factor) to Ciprofloxacin or Levofloxacin instead (which were previously NOT known as a risk factor). The British Thoracic Society guidelines (1998) for community acquired pneumonia (CAP) suggested changing from using Cefuroxime PLUS Clarithromycin for severe CAP to using Benzylpenicillin PLUS Levofloxacin instead, to lessen the risk.
For a while this change seemed to reduce the number of C. difficile cases but sure enough over time it came back. The new strain of bacterium O27, affecting not only Quebec but also the rest of the Western World, had developed resistance to the fluoroquinolones. It was therefore logical to assume that the change towards the increased use of fluoroquinolones “selected” out the O27 strain, by eliminating those strains sensitive to fluoroquinolones yet allowing the resistant strain to survive unimpeded. In addition the O27 strain was a hyper-producer of the toxin which caused the severe diarrhoea in C. difficile infection, adding to severity and transmission.
Yes, yes, I guess we all know this!!! But do you know that a team from Baylor College of Medicine in Houston, Texas, have another theory as to why the O27 strain emerged; they blame the sugar trehalose. Yeah sugar again…it rots our teeth, makes us fat and is addictive…
What is trehalose?
Trehalose is a disaccharide formed from two units of glucose. In the gut it is broken down by the enzyme trehalase (Remember: anything in science that ends in “-ase” is an enzyme) in the brush border of the intestinal mucosa into the two separate units of glucose. It is not quite as sweet as the sugar sucrose but it is often used as a sweetener in the food industry because it lowers the freezing point of food, apparently especially in ice cream (…and I do like ice cream!).
The increased supplementation of food with trehalose coincided with a spike in cases of C. difficile, so could there be a connection? Is this just a coincidence or does increased trehalose have an effect on O27 C. difficile?
Trehalose and O27 C. difficile
The researchers in Texas first showed that O27 C. difficile grew 5 times better than non-O27 strains when trehalose was available. This would give a clear advantage for the O27 strain when trying to out-compete its rivals.
The O27 strain was also shown to produce much more trehalase than non-O27 strains because of a single mutation in a repressor gene which normally stops the bacterium producing this enzyme. As a result O27 was able to use trehalase as an energy source much more effectively than the non-O27 strains.
Studies on mice were then performed using the same strain of O27 C. difficile where the only difference was that one group of mice had the O27 which produced more trehalase and the other group had the same O27 which had been genetically modified so that it couldn’t produce trehalase. The strains of O27 were otherwise identical. This experiment showed that infection with O27 C. difficile that produced trehalase was much more severe, and had a higher mortality, than the O27 which didn’t produce trehalase.
A second experiment compared mice with the trehalase producing O27 strain of C. difficile given trehalose in their diet versus a group who received no trehalose. The amount of toxin produced by the bacterium and the mortality was much higher in the group who received dietary trehalose.
So the two experiments in mice show that dietary trehalose can increase the mortality from C. difficile… at least in (ice cream eating) mice.
A final experiment by the researchers in Texas looked at ileostomy fluid from people eating a “normal” diet but one which contained trehalose. Ileostomy fluid represents the normal bowel fluid as it enters the colon; if trehalose does not make it to the colon it cannot be responsible C. difficile as C. difficile is a condition that occurs within the colon. Their experiment showed there was plenty of trehalose in the ileostomy fluid to cause a reaction in O27 C. difficile.
So what have the researchers discovered?
The researchers in Texas have discovered that O27 C. difficile:
- Grows better in the presence of trehalose than non-O27
- Is better at using trehalose than non-O27
- Causes more severe infection in the presence of trehalose than non-O27
- Is activated in the colon by “normal” dietary amounts of trehalose
And all of this coincides with the international spread of O27 C. difficile.
But could this just represent the recent evolution of O27 C. difficile enabling it to be able to use trehalose? Well it turns out that O27 C. difficile has been around since at least 1985 when it was first identified as causing an infection in Paris. Since then there have been sporadic cases reported, including a case in Minnesota, but no outbreaks until 2000-2003. Both of these isolates (Paris and Minnesota) have the same resistance to fluoroquinolones, the same hyper-production of toxin and the increased ability to use trehalose as the Quebec outbreak strain and yet they never really spread. Dun dun dah!!!
OK quit the melodramatic music, it could be that we just weren’t using enough fluoroquinolones pre-2000 to select out O27 C. difficile from the other strains of bacteria, but I think this is unlikely as fluoroquinolones have been used in large amounts for many years and a change in prescribing habits would be more gradual than the sudden 2003 outbreak of O27. It is more likely that something else changed quickly to cause the outbreak and if it wasn’t the bacterium itself it may well have been the environment the bacterium was living in… say an energy source that gave O27 a competitive advantage… which also made O27 more virulent… say something like the increase of trehalose in our diets? Like the double helping of ice-cream I like to eat!
Dietary trehalose enhances virulence of epidemic Clostridium difficile. Collins J., Robinson C., Danhof H., et al. Nature 2018, Vol. 553; 291-294