Clostridium difficile is the most common healthcare-associated infection in the United States. In the United States alone, C difficileinfection (CDI) causes approximately 500,000 infections and 30,000 deaths annually.1 In the early 2000s, a substantial increase in CDI incidence and severity were noted in both the United States and Canada.2 Further investigation indicated that a particular C difficile strain, known as ribotype (RT) 027, was causing the majority of CDIs in both countries. Compared with previous endemic strains, this strain was found to be resistant to fluoroquinolones and to produce a novel binary toxin. In addition, RT027 also had acquired a loss-of-function mutation in tcdC, a negative regulator of the production of toxins A and B. Several microbiologic characteristics were posited to lead to the emergence and global dissemination of RT027, including fluoroquinolone resistance, particularly in the setting of widely increasing fluoroquinolone use in adults, and potentially increased sporulation efficiency. In subsequent years, the emergence of RT078 was noted. Despite their phylogenetic distance, like RT027, RT078 produces binary toxin and has the same tcdC mutation, although fluoroquinolone resistance is less common. Because of the identification of genetically similar strains of RT078 in livestock and humans, the role of animals and foods as potential reservoirs of RT078 has been proposed.
In the January 2018 issue of Nature,3 Robert Britton, PhD, of the department of molecular virology and microbiology, Baylor College of Medicine in Houston, Texas, and colleagues presented an intriguing alternative explanation for the emergence and dissemination of these 2 epidemic strains of C difficile. In that landmark study, Britton, et al provided compelling epidemiologic, microbiologic, and genomic data strongly suggesting the role of dietary trehalose in providing C difficile RT027 and RT078 a selective advantage over endemic strains. Trehalose, a naturally occurring sugar found in honey, mushrooms, and shellfish, is a disaccharide composed of 2 glucose molecules. In the food manufacturing industry, trehalose has several advantages over other sweeteners, such as improving the stability and texture of foods, largely related to the relative stability of trehalose to high temperatures and acid hydrolysis. The expanded use of trehalose in the food manufacturing industry began in the United States, Europe, and Canada in approximately 2000, 2001, and 2005, respectively. Trehalose is now an additive found in several commonly consumed foods, including pasta, beef, and ice cream.
Of note, the timeline of expanded dietary trehalose coincides with the rise of CDI, particularly the rise of infections caused by RT027 and RT078. Britton and colleagues have investigated this interesting ecological observation through their identification of a mechanism of C difficile trehalose metabolism. All C difficile strains can utilize trehalose as a carbon source through the activity of a phosphotrehalase enzyme encoded by the treA gene. However, compared with other C difficilestrains, RT027 and RT078 are able to grow robustly at low concentrations of trehalose. This enhanced growth seems to be related to genetic modifications in genes that contribute to trehalose metabolism, although the specific genetic modifications in RT027 and RT078 are quite different. RT027 has acquired a mutation in the gene that represses treA, leading to excess production of treA in the presence of trehalose, resulting in more efficient trehalose utilization by RT027 strains.
The importance of treA in C difficile pathogenesis was confirmed in an animal model of infection in which animals infected with a genetically modified RT027 strain that was missing the treA gene had improved outcomes compared with animals infected with the wild type RT027 strain. RT078, on the other hand, does not have a mutated treA repressor gene. Instead, RT078 has uniquely acquired 4 additional genes that allow it to metabolize trehalose more efficiently. Thus, the identification of 2 distinct genetic modifications that augment the same biochemical pathway strongly supports the role of dietary trehalose in the increased incidence of CDI caused by RT027 and RT078.
While these epidemiologic, microbiologic, and genomic data are compelling, several other epidemiologic observations suggest that other factors in addition to dietary trehalose likely contributed to the observed shifts in CDI clinical and molecular epidemiology. For example, in Canada, the outbreak of RT027 in 2002 predated expanded use of trehalose in 2005. Furthermore, recent data from the US Centers for Disease Control and Prevention (CDC) suggest that RT027 is declining, and RT078 is relatively uncommon, despite no active measures being taken to reduce dietary trehalose.4 Furthermore, compared with adults, RT027 and RT078 have not predominated in pediatric populations, although pediatric molecular epidemiologic investigation is quite limited. Thus, while dietary trehalose may provide a selective advantage to these epidemic strains, there also appear to be other factors that have contributed to the observed shifts in CDI clinical and molecular epidemiology.
The clinical implications of this finding are currently unknown. While therapeutic options for CDI have expanded in recent years with the development of narrow-spectrum antibiotics (eg, fidaxomicin), immunologics (eg, monoclonal antibody against toxin B), and biotherapeutics (eg, fecal microbiota transplantation), the frequency of severe and/or recurrent CDI remains unacceptably high.5 Thus, there remains a need for novel therapeutic strategies, such as a low-trehalose diet, for CDI treatment and prevention, and this is a potential area of future clinical investigation. The clinical benefit of such strategies should be proven before wide-scale changes to trehalose use in food manufacturing are undertaken.