In the early 2000s an intestinal superbug began quietly spreading through hospitals around the world causing a deadly form of diarrhea among immune-compromised patients. At the same time, a breakthrough by food scientists allowed processing of a new sugar substitute called trehalose, used in many kinds of processed food. Today, surprising new evidence has uncovered a seemingly unlikely link explaining the terrifying increase in persistent Clostridium difficile infections and the food additive trehalose.
The C. difficile microbe is an intestinal pathogen that mimics the symptoms of food poisoning. It can be mistaken for food poisoning but last much longer leading to more serious gastrointestinal disease and possibly death if left untreated. Ironically the cause of C. difficile infection may be due to antibiotic use. As antibiotics are supposed to kill bad bacteria that make us sick, an unfortunate victim are also the good bacteria in our digestive tract, the innocent bystanders. Once these commensal bacteria are wiped out C. difficile has free reign to grow uncontrolled. These infections in immune-compromised patients are very difficult to treat and antibiotic therapies only exacerbate the infection.
Also, part of this story is the emergence of a sugar substitute called trehalose. The mass consumption of trehalose was sparked by a sudden drop in the cost of its manufacturing at the turn of the century after researchers in Japan engineered a bioprocessing pathway that made its production 200x cheaper. This generated a massive influx of the disaccharide into processed foods and today it can be found in anything from ice cream to ground beef.
At about the same time trehalose was flooding into the food market, two epidemic strains of C. difficile called RT027 and RT078 were rising to become the deadliest strains of C. difficile infection. At least one of the strains RT027 also contained resistance to the wide spectrum antibiotic fluoroquinolone but this was known since the mid-’80s. So, what was making these strains so terrifyingly virulent and persistent?
Researchers analyzing RT027 and RT078 identified unique mutations in each strain compared to non-epidemic lineages. Sequencing RT027 genomes revealed a single nucleotide mutation in the gene controlling trehalose metabolism while sequencing RT078 revealed something completely different, an entire second copy of genes responsible for trehalose uptake and metabolism. The commonality among these two strains was their unique ability to metabolize trehalose as a nutrient source.
Experiments showed these strains could not only survive but also grow using significantly smaller amounts of trehalose compared to other strains of C. difficile that could essentially only survive on glucose. In animal models, humanized mice containing human microbiota in their intestinal tract were infected with the RT028 strain. The researchers found the group fed a consistent diet of trehalose at levels obtained in a typical meal, had significantly higher mortality compared to a second control group fed water. Furthermore, in competition experiments, RT078 was observed to outcompete bacteria growing in a human fecal mini-bioreactor model containing trehalose. In contrast, a knockout strain of RT078 missing its trehalose uptake gene failed to outcompete bacteria in the same model system.
A final set of experiments involved measuring the activation of trehalose metabolism in C. difficile infected mice. Just a single dose of the disaccharide, equivalent to a serving of ice cream, triggered greater than 1000-times the expression of trehalose metabolism in RT027 compared to a non-epidemic strain of C. difficile.
Lastly, the researchers collected intestinal fluids from 3 anonymous human donors and found that it contained enough trehalose to activate trehalose metabolizing genes in RT027.
Together these results showed that trehalose consumption was a trigger factor in selecting more dominant strains of C. difficile with greater virulence leading to greater mortality.
Roughly 1-3% of healthy adults carry C. difficile among their normal intestinal bacteria. However, once the balance of gut flora is disturbed for example by a course of antibiotics, this can wipe out normal bacteria leaving C. difficile to overtake the gut flora. In combination with the influx of trehalose into processed foods two epidemic strains of C. difficile, RT027 and RT078 emerged as the dominant infectious strains each containing unique mechanisms of trehalose metabolism. These findings link the increased consumption of trehalose in the human diet to the emergence of exceedingly virulent epidemic strains of C. difficile. In addition to antibiotics exacerbating C. difficile infections it now seems that sugars can also be added to the list.
From: J. Collins et al., Nature, 2018, 553, 291-294
Dr. Dinesh Fernando