Recent studies have shown that individuals with colorectal cancer have an altered gut microbiome compared to healthy controls. It remains unclear whether these differences are a response to tumorigenesis or actively drive tumorigenesis. To determine the role of the gut microbiome in the development of colorectal cancer, we characterized the gut microbiome in a murine model of inflammation-associated colorectal cancer that mirrors what is seen in humans. We followed the development of an abnormal microbial community structure associated with inflammation and tumorigenesis in the colon. Tumor-bearing mice showed enrichment in operational taxonomic units (OTUs) affiliated with members of the Bacteroides, Odoribacter, and Akkermansia genera and decreases in OTUs affiliated with members of the Prevotellaceae and Porphyromonadaceae families. Conventionalization of germfree mice with microbiota from tumor-bearing mice significantly increased tumorigenesis in the colon compared to that for animals colonized with a healthy gut microbiome from untreated mice. Furthermore, at the end of the model, germfree mice colonized with microbiota from tumor-bearing mice harbored a higher relative abundance of populations associated with tumor formation in conventional animals. Manipulation of the gut microbiome with antibiotics resulted in a dramatic decrease in both the number and size of tumors. Our results demonstrate that changes in the gut microbiome associated with inflammation and tumorigenesis directly contribute to tumorigenesis and suggest that interventions affecting the composition of the microbiome may be a strategy to prevent the development of colon cancer.

Recent studies have suggested that the gut microbiome may be an important factor in the development of colorectal cancer (CRC). Abnormalities in the gut microbiome have been reported in patients with CRC; however, this microbial community has not been explored as a potential screen for early stage disease. We characterized the gut microbiome in patients from three clinical groups representing the stages of CRC development: health, adenoma, and carcinoma. Analysis of the gut microbiome from stool samples revealed both an enrichment and depletion of several bacterial populations associated with adenomas and carcinomas. Combined with known clinical risk factors of CRC (e.g. BMI, age, race), data from the gut microbiome significantly improved the ability to differentiate between healthy, adenoma, and carcinoma clinical groups relative to risk factors alone. Using Bayesian methods, we determined that using gut microbiome data as a screening tool improved the pre-test to post-test probability of adenoma over 50-fold. For example, the pre-test probability in a 65 year-old was 0.17% and, after using the microbiome data, this increased to 10.67% (1 in 9 chance of having an adenoma). Taken together the results of our study demonstrate the feasibility of using the composition of the gut microbiome to detect the presence of precancerous and cancerous lesions. Furthermore, these results support the need for more cross sectional studies with diverse populations and linkage to other stool markers, dietary data, and personal health information.

BackgroundA growing body of evidence indicates that the gut microbiome plays a role in the development of colorectal cancer (CRC). Patients with CRC harbor gut microbiomes that are structurally distinct from those of healthy individuals; however, without the ability to track individuals during disease progression, it has not been possible to observe changes in the microbiome over the course of tumorigenesis. Mouse models have demonstrated that these changes can further promote colonic tumorigenesis. However, these models have relied upon mouse-adapted bacterial populations and so it remains unclear which human-adapted bacterial populations are responsible for modulating tumorigenesis.ResultsWe transplanted fecal microbiota from three CRC patients and three healthy individuals into germ-free mice, resulting in six structurally distinct microbial communities. Subjecting these mice to a chemically induced model of CRC resulted in different levels of tumorigenesis between mice. Differences in the number of tumors were strongly associated with the baseline microbiome structure in mice, but not with the cancer status of the human donors. Partitioning of baseline communities into enterotypes by Dirichlet multinomial mixture modeling resulted in three enterotypes that corresponded with tumor burden. The taxa most strongly positively correlated with increased tumor burden were members of the Bacteroides, Parabacteroides, Alistipes, and Akkermansia, all of which are Gram-negative. Members of the Gram-positive Clostridiales, including multiple members of Clostridium Group XIVa, were strongly negatively correlated with tumors. Analysis of the inferred metagenome of each community revealed a negative correlation between tumor count and the potential for butyrate production, and a positive correlation between tumor count and the capacity for host glycan degradation. Despite harboring distinct gut communities, all mice underwent conserved structural changes over the course of the model. The extent of these changes was also correlated with tumor incidence.ConclusionOur results suggest that the initial structure of the microbiome determines susceptibility to colonic tumorigenesis. There appear to be opposing roles for certain Gram-negative (Bacteroidales and Verrucomicrobia) and Gram-positive (Clostridiales) bacteria in tumor susceptibility. Thus, the impact of community structure is potentially mediated by the balance between protective, butyrate-producing populations and inflammatory, mucin-degrading populations.

The S100 family of EF-hand calcium (Ca 2؉ )-binding proteins is essential for a wide range of cellular functions. During infection, certain S100 proteins act as damage-associated molecular patterns (DAMPs) and interact with pattern recognition receptors to modulate inflammatory responses. In addition, these inflammatory S100 proteins have potent antimicrobial properties and are essential components of the immune response to invading pathogens. In this review, we focus on S100 proteins that exhibit antimicrobial properties through the process of metal limitation, termed nutritional immunity, and discuss several recent advances in our understanding of S100 protein-mediated metal sequestration at the site of infection. S100 proteins are EF-hand Ca 2ϩ -binding proteins involved in a diverse array of both intracellular and extracellular regulatory functions (1-6). Over 20 S100 proteins have been identified, and all have a characteristic dimeric structure distinct from other EF-hand proteins (7). Like many EF-hand proteins, Ca 2ϩ signaling function is associated with a binding-induced conformational change exposing a hydrophobic patch that generates specificity for target proteins (8,9). Within the cell, S100 proteins regulate numerous important processes including Ca 2ϩ homeostasis, energy metabolism, and cell proliferation and differentiation. Remarkably, certain S100 proteins can be secreted and/or released by cells, and among these, some play an important role during infection and inflammation (1). In particular, extracellular S100 proteins can act as damage-associated molecular pattern (DAMP) 3 proteins and initiate a proinflammatory immune response through interaction with pattern recognition receptors and the receptor for advanced glycation end products (RAGE) (10, 11). Furthermore, through the process of nutrient metal limitation, several S100 proteins have been shown to be antimicrobial and play a key role in host defense at the host-pathogen interface (12)(13)(14)(15)(16)(17). In this review, we provide insight into structure and function of the three S100 proteins with antimicrobial and inflammatory properties: S100A7 (psoriasin); S100A8/S100A9 (calprotectin; calgranulin A and B; MRP-8 and 9); and S100A12 (calgranulin C). Key Properties of S100 Proteins with Antimicrobial Activity Structure and Metal BindingThe basic unit of EF-hand proteins is a helix-Ca 2ϩ binding loop-helix motif; these motifs are typically packed in pairs to form a stable globular four-helix bundle domain (8). Each S100 protein contains a distinctive S100-specific N-terminal EFhand motif and a C-terminal canonical EF-hand motif (Fig. 1). The fundamental structural unit of S100 proteins is a highly integrated antiparallel dimer (7); all S100 proteins form this structure as homodimers, and some will also heterodimerize. S100A8 and S100A9 are unique among all members of the family because they preferentially form a heterodimer (18), which is termed calprotectin based on its role in innate immunity. S100 proteins are also known to form high...

Clostridium difficile is the most commonly reported nosocomial pathogen in the United States and is an urgent public health concern worldwide1. Over the past decade, incidence, severity, and costs associated with C. difficile infection (CDI) have increased dramatically2. CDI is most commonly initiated by antibiotic-mediated disruption of the gut microbiota; however, non-antibiotic associated CDI cases are well documented and on the rise3,4. This suggests that unexplored environmental, nutrient, and host factors likely influence CDI. Here we show that excess dietary zinc (Zn) significantly alters the gut microbiota and in turn reduces the threshold of antibiotics needed to confer susceptibility to C. difficile infection. In mice colonized with C. difficile, excess dietary Zn severely exacerbates C. difficile-associated disease by increasing toxin activity and altering the host immune response. In addition, we show that the Zn binding S100 protein calprotectin is antimicrobial against C. difficile and an essential component of the innate immune response to CDI. Together, these data suggest that nutrient Zn levels play a key role in determining susceptibility to CDI and severity of disease, and that calprotectin-mediated metal limitation is an important factor in the host immune response to C. difficile.

These authors contributed equally to this work.

Trusted evidence. Informed decisions. Better health.

Mounting evidence indicates that alterations to the gut microbiota, the complex community of bacteria that inhabits the gastrointestinal tract, are strongly associated with the development of colorectal cancer. We used antibiotic perturbations to a murine model of inflammation-driven colon cancer to generate eight starting communities that resulted in various severities of tumorigenesis. Furthermore, we were able to quantitatively predict the final number of tumors on the basis of the initial composition of the gut microbiota. These results further bolster the evidence that the gut microbiota is involved in mediating the development of colorectal cancer. As a final proof of principle, we showed that perturbing the gut microbiota in the midst of tumorigenesis could halt the formation of additional tumors. Together, alteration of the gut microbiota may be a useful therapeutic approach to preventing and altering the trajectory of colorectal cancer.