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The increasing frequency and severity of healthcare-associated outbreaks caused by bacterium Clostridium difficile have been linked to the widely used food additive trehalose. A team of researchers discovered that in laboratory tests and animal models, trehalose enhances the virulence of epidemic C. difficile lineages that predominate in patient infections.
C. difficile infections have always been a problem in hospitals, but during the last decade they have become the most common cause of hospital-acquired infections in developed countries. According to the Center for Disease Control and Prevention, C. difficile is a major cause of infectious disease-related death. In 2015, the CDC reported that C. difficile caused almost a half-million infections in patients.
The bacteria cause life-threatening inflammation of the colon and diarrhea. Patients 65 years and older are at most risk, and most infections occur in people who have received medical care and antibiotics. C. difficile lineages RT027 and RT078 have become dominant more recently across the globe. These lineages have been present in people for years without causing major outbreaks; in the 1980s they were not epidemic or hypervirulent but after the year 2000 they began to predominate and cause major outbreaks.
Resistance to fluoroquinolone antibiotics is likely one of the factors that is helping lineage RT027 cause epidemics. However, fluoroquinolone resistance is also a characteristic of other C. difficile lineages that are not epidemic. The researchers investigated what sources of food RT027 and RT078 preferred. They discovered that these lineages can grow on levels of sugar trehalose that are about 1,000 times lower than those needed by other lineages of these bacteria, giving RT027 and RT078 a major advantage.
Each lineage is highly efficient at using trehalose and evolved independent mechanisms to utilize this sugar. To connect the ability to metabolize low levels of trehalose with increased disease severity, the researchers worked with a mouse model of C. difficile infection. Mice received a strain of the RT027 lineage of C. difficile and a diet with or without low trehalose levels. What the mice ate made a difference to the virulence of the infection; mortality was higher in the group consuming trehalose.
Further experiments showed that increased disease severity in the presence of trehalose could not be explained by the mice having higher numbers of bacteria, instead what made the disease more severe was that RT027 produced higher levels of toxins. These and other experiments provide evidence that dietary trehalose has contributed to the predominance of epidemic C. difficile lineages and to their virulence.
Because the genetic factors that allow these bacteria to metabolize trehalose and increase the production of toxins were present well before the outbreaks started, the researchers investigated what could have triggered the epidemics. 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 three years later the reports of outbreaks with these lineages started to increase.
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