Ask the Doctors

Dear Doctor: I recently read about a sugar additive being linked to the rise of a killer bug. What is this additive, how do I avoid it, and how serious is the threat?

Dear Reader: Clostridium difficile, or C. diff, is a bacterium that can cause severe intestinal infections, leading to severe diarrhea, possible hospitalizations and even death, especially in people over the age of 65. Antibiotic use is often the precipitating factor in C. diff infections because the drugs kill off the normal bacterial populations in the colon and allow for C. diff to multiply and release toxins, triggering inflammation and diarrhea. Rates of C. diff infection are increasing in this country, with nearly 500,000 people per year affected and 15,000 deaths. Use and overuse of antibiotics are blamed for this increase. But a recent study in the journal Nature may point to another factor.

First, note that C. diff has different subtypes, or ribotypes, with two strains in particular -- RT027 and RT078 -- associated with large outbreaks of disease. These outbreaks have been common since the year 2000. The year is important because that's when the sugar trehalose became available for mass production and began to be readily placed in foods and drinks. Of course, many notable things occurred in the year 2000, so let's explore how a sugar product could specifically be blamed for an increase in the risk of C. diff outbreaks.

Trehalose is a naturally occurring sugar produced by plants, fungi, bacteria and insects that helps organisms retain water and prevents cellular damage when there is no water. It's about 45 percent as sweet as sucrose (or table sugar), but researchers for years lacked a cost-effective way to extract it. However, in 2000, a new enzymatic extraction method led to a cheap way to mass-produce trehalose. Subsequently, many food products and drinks were produced with this sugar as an ingredient.

The study you are referencing looked at how the C. diff ribotypes RT027 and RT078 respond to trehalose. For starters, RT027 will grow five times greater than other ribotypes of C. diff when trehalose is a food source. Also, RT027 needs lower concentrations of trehalose to turn on enzymes that metabolize the sugar. Mice infected with the RT027 type were three times as likely to die when given a solution that mimicked human intake of trehalose compared with those given water. The ribotype RT078 also shows an increased ability to metabolize trehalose.

Further, the small intestine doesn't absorb trehalose as well as it does sucrose. This leads to more trehalose ending up in the large intestine, which is where C. diff causes its damage. Thus, if a patient has an RT027 or RT078 strain of C. diff and trehalose is present in the large intestine, the bacteria can readily use trehalose to survive and multiply. These bacteria will also have a competitive advantage over other bacteria in the colon that cannot utilize trehalose.

It's one of those quirks of nature that a bacterium can use a naturally occurring substance to its benefit -- and our detriment. I would look at food labels and evaluate whether your diet is high in this sugar. If so, you might want to make adjustments. The data are concerning.

(Send your questions to askthedoctors@mednet.ucla.edu, or write: Ask the Doctors, c/o Media Relations, UCLA Health, 924 Westwood Blvd., Suite 350, Los Angeles, CA, 90095. Owing to the volume of mail, personal replies cannot be provided.)

More like Ask the Doctors