Common sugar additive triggered C. difficile outbreaks, study suggests

Widespread use of trehalose—a sugary food additive found in pasta, ice cream, and sports drinks—has likely spurred epidemic outbreaks of virulent strains of Clostridium difficile, according to results of a recent study published in Nature.

“Our group and others have found that C. difficile lineages RT027 and RT078 have become dominant more recently around the globe,” said first author James Collins, PhD, postdoctoral associate in the Alkek Center for Metagenomics and Microbiome Research, Baylor College of Medicine, Houston, TX.

“These lineages have been present in people for years without causing major outbreaks,” Dr. Collins explained. “In the 1980s, they were not epidemic or hypervirulent, but after the year 2000 they began to predominate and cause major outbreaks.”

“We wanted to know what had helped these lineages become a major health risk,” he said.

To find out, Dr. Collins and colleagues tested an RT027 isolate against a panel of energy sources (carbon source utilization test) to see which source would increase its growth. The test showed that trehalose increased the isolate’s growth by fivefold compared with a non-RT027 strain.

Further testing with other C. difficile isolates revealed that only epidemic RT027 and RT078 strains exhibited enhanced growth with trehalose.

“In 2000, trehalose was approved as a food additive in the United States for a number of foods from sushi and vegetables to ice cream, and about 3 years later the reports of outbreaks with these lineages [RT027 and RT078] started to increase,” said corresponding author Robert Britton, PhD, professor of molecular virology and microbiology at Baylor College of Medicine. “Other factors may also contribute, but we think that trehalose is a key trigger.”

Generally recognized as safe?

Trehalose, like sucrose (table sugar), is a disaccharide and a naturally occurring sugar, but is only half as sweet as sucrose. It’s used to retain food stability, prevent foods from drying out, and enhance their texture. Trehalose has been available for years, but it wasn’t until about 2000 that a Japanese manufacturer found a way to affordably mass-produce it. At that time, the Food and Drug Administration granted it “generally recognized as safe” status as a food additive.

“An important contribution of this study is the realization that what we once considered a perfectly safe sugar for human consumption can have unexpected consequences,” Dr. Collins said.

To learn how trehalose could be linked to C. difficile to increase disease severity, the researchers performed different experiments in mice.

“Mice received a strain of the RT027 lineage of C. difficile and a diet with or without low trehalose levels,” Dr. Collins explained. “What the mice ate made a difference to the virulence of the infection; mortality was higher in the group consuming trehalose.”

Further experiments with trehalose showed that disease severity hadn’t increased because the mice had higher numbers of bacteria but because RT027 had produced higher levels of toxins.

How does this happen? The investigators discovered that RT027 developed a genetic mutation that allows the bacterium to sense trehalose and produce an enzyme to metabolize it for food, even at extremely low concentrations. In addition, they found that RT078 acquired a cluster of four genes involved in the metabolism of trehalose, allowing the strain to grow exceptionally well on low levels of the sugar.

“This shows the two C. diff strains have adapted to feed on trehalose in two completely different ways!” wrote Francis S. Collins, MD, PhD, director of the National Institutes of Health, which funded the study.

The findings indicate that the widespread adoption and use of trehalose in the human diet has played a significant role in the emergence of epidemic and hypervirulent C. difficile strains, the researchers concluded.