Colorectal cancer is the result of multiple genetic mutations that drive normal cells to adenoma and then carcinoma. Recent technology has evolved to allow for an in-depth examination of the ...microbiota and it has become clear that many components of the intestinal microbiome play a role in promoting carcinogenesis. This review aims to describe the potential mechanisms that lead to the dysbiosis that initiates tumor formation and that influence the development of cancer recurrence following surgical resection. We further discuss how manipulation of the microbiome may be a future novel strategy to prevent both primary and secondary colorectal cancer. While we discuss how bacterial communities and individual strains can promote cancer, the microbiome is individualized, dynamic, and complex, and our understanding of its role in carcinogenesis is still in its infancy.
The bacteria that colonize humans and our built environments have the potential to influence our health. Microbial communities associated with seven families and their homes over 6 weeks were ...assessed, including three families that moved their home. Microbial communities differed substantially among homes, and the home microbiome was largely sourced from humans. The microbiota in each home were identifiable by family. Network analysis identified humans as the primary bacterial vector, and a Bayesian method significantly matched individuals to their dwellings. Draft genomes of potential human pathogens observed on a kitchen counter could be matched to the hands of occupants. After a house move, the microbial community in the new house rapidly converged on the microbial community of the occupants’ former house, suggesting rapid colonization by the family’s microbiota.
The microorganisms that inhabit hospitals may influence patient recovery and outcome, although the complexity and diversity of these bacterial communities can confound our ability to focus on ...potential pathogens in isolation. To develop a community-level understanding of how microorganisms colonize and move through the hospital environment, we characterized the bacterial dynamics among hospital surfaces, patients, and staff over the course of 1 year as a new hospital became operational. The bacteria in patient rooms, particularly on bedrails, consistently resembled the skin microbiota of the patient occupying the room. Bacterial communities on patients and room surfaces became increasingly similar over the course of a patient's stay. Temporal correlations in community structure demonstrated that patients initially acquired room-associated taxa that predated their stay but that their own microbial signatures began to influence the room community structure over time. The α- and β-diversity of patient skin samples were only weakly or nonsignificantly associated with clinical factors such as chemotherapy, antibiotic usage, and surgical recovery, and no factor except for ambulatory status affected microbial similarity between the microbiotas of a patient and their room. Metagenomic analyses revealed that genes conferring antimicrobial resistance were consistently more abundant on room surfaces than on the skin of the patients inhabiting those rooms. In addition, persistent unique genotypes of
and
were identified. Dynamic Bayesian network analysis suggested that hospital staff were more likely to be a source of bacteria on the skin of patients than the reverse but that there were no universal patterns of transmission across patient rooms.
The most feared complication following intestinal resection is anastomotic leakage. In high risk areas (esophagus/rectum) where neoadjuvant chemoradiation is used, the incidence of anastomotic leaks ...remains unacceptably high (≈ 10%) even when performed by specialist surgeons in high volume centers. The aims of this study were to test the hypothesis that anastomotic leakage develops when pathogens colonizing anastomotic sites become in vivo transformed to express a tissue destroying phenotype. We developed a novel model of anastomotic leak in which rats were exposed to pre-operative radiation as in cancer surgery, underwent distal colon resection and then were intestinally inoculated with Pseudomonas aeruginosa, a common colonizer of the radiated intestine. Results demonstrated that intestinal tissues exposed to preoperative radiation developed a significant incidence of anastomotic leak (>60%; p<0.01) when colonized by P. aeruginosa compared to radiated tissues alone (0%). Phenotype analysis comparing the original inoculating strain (MPAO1- termed P1) and the strain retrieved from leaking anastomotic tissues (termed P2) demonstrated that P2 was altered in pyocyanin production and displayed enhanced collagenase activity, high swarming motility, and a destructive phenotype against cultured intestinal epithelial cells (i.e. apoptosis, barrier function, cytolysis). Comparative genotype analysis between P1 and P2 revealed a single nucleotide polymorphism (SNP) mutation in the mexT gene that led to a stop codon resulting in a non-functional truncated protein. Replacement of the mutated mexT gene in P2 with mexT from the original parental strain P1 led to reversion of P2 to the P1 phenotype. No spontaneous transformation was detected during 20 passages in TSB media. Use of a novel virulence suppressing compound PEG/Pi prevented P. aeruginosa transformation to the tissue destructive phenotype and prevented anastomotic leak in rats. This work demonstrates that in vivo transformation of microbial pathogens to a tissue destroying phenotype may have important implications in the pathogenesis of anastomotic leak.
Introduction
Colorectal anastomotic leak, a feared complication, results in significantly increased patient morbidity, mortality, and hospital resource utilization. The overall incidence of ...colorectal anastomotic leak is approximately 11 % with increasing rate the closer the anastomosis is to the anal verge. Because surgeons are unable to reliably predict which anastomosis would fail, most will construct a diverting ileostomy for low colorectal anastomosis to circumvent the devastating complications of anastomotic failure. Despite extensive investigations on technical considerations of anastomosis construction, anastomotic leaks continue to occur at an unacceptably high rate.
Discussion
In this review, we examine the major known risk factors and technical considerations that have been implicated as factors in leakage. Although surgical technique has evolved over the past several decades with the advent of newer surgical staplers, laparoscopy, and robotics, we have not witnessed a decrease in the incidence of colorectal anastomotic leaks suggesting that the fundamental pathogenesis of anastomotic leak remains unknown. Among the factors contributing to anastomotic healing, intestinal bacteria remains largely overlooked even though compelling evidence exist that intraluminal microbes could play a major role in pathogenesis of anastomotic leak. Further investigation focusing on intestinal microbes could be one such avenue for uncovering the elusive cause of colorectal anastomotic leak.
The Western diet, which is high in fat, is a modifiable risk factor for colorectal recurrence after curative resection. We investigated the mechanisms by which the Western diet promotes tumor ...recurrence, including changes in the microbiome, in mice that underwent colorectal resection.
BALB/c male mice were fed either standard chow diet or Western-type diet (characterized by high fat, no fiber, and decreased minerals and vitamins) for 4 weeks; some mice were given antibiotics or ABA-PEG20k-Pi20 (Pi-PEG), which inhibits collagenase production by bacteria, but not bacterial growth, in drinking water. Colorectal resections and anastomoses were then performed. The first day after surgery, mice were given enemas containing a collagenolytic rodent-derived strain of Enterococcus faecalis (strain E2), and on the second day they were given mouse colon carcinoma cells (CT26). Twenty-one days later, distal colons were removed, and colon contents (feces, distal colon, and tumor) were collected. Colon tissues were analyzed by histology for the presence of collagenolytic colonies and by 16S ribosomal RNA sequencing, which determined the anatomic distribution of E faecalis at the site of the anastomosis and within tumors using in situ hybridization. Mouse imaging analyses were used to identify metastases.
Colorectal tumors were found in 88% of mice fed the Western diet and given antibiotics, surgery, and E faecalis compared with only 30% of mice fed the standard diet followed by the same procedures. Colon tumor formation correlated with the presence of collagenolytic E faecalis and Proteus mirabilis. Antibiotics eliminated collagenolytic E faecalis and P mirabilis but did not reduce tumor formation. However, antibiotics promoted emergence of Candida parapsilosis, a collagenase-producing microorganism. Administration of a Pi-PEG reduced tumor formation and maintained diversity of the colon microbiome.
We identified a mechanisms by which diet and antibiotic use can promote tumorigenesis by colon cancer cells at the anastomosis after colorectal surgery. Strategies to prevent emergence of these microbe communities or their enzymatic activities might be used to reduce the risk of tumor recurrence in patients undergoing colorectal cancer surgery.
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Even under the most expert care, a properly constructed intestinal anastomosis can fail to heal, resulting in leakage of its contents, peritonitis, and sepsis. The cause of anastomotic leak remains ...unknown, and its incidence has not changed in decades. We demonstrate that the commensal bacterium Enterococcus faecalis contributes to the pathogenesis of anastomotic leak through its capacity to degrade collagen and to activate tissue matrix metalloproteinase 9 (MMP9) in host intestinal tissues. We demonstrate in rats that leaking anastomotic tissues were colonized by E. faecalis strains that showed an increased collagen-degrading activity and also an increased ability to activate host MMP9, both of which contributed to anastomotic leakage. We demonstrate that the E. faecalis genes gelE and sprE were required for E. faecalis-mediated MMP9 activation. Either elimination of E. faecalis strains through direct topical antibiotics applied to rat intestinal tissues or pharmacological suppression of intestinal MMP9 activation prevented anastomotic leak in rats. In contrast, the standard recommended intravenous antibiotics used in patients undergoing colorectal surgery did not eliminate E. faecalis at anastomotic tissues nor did they prevent leak in our rat model. Finally, we show in humans undergoing colon surgery and treated with the standard recommended intravenous antibiotics that their anastomotic tissues still contained E. faecalis and other bacterial strains with collagen-degrading/MMP9-activating activity. We suggest that intestinal microbes with the capacity to produce collagenases and to activate host metalloproteinase MMP9 may break down collagen in the intestinal tissue contributing to anastomotic leak.
Much about the role of intestinal microbes at the site of colon cancer development and tumor progression following curative resection remains to be understood. We have recently shown that ...collagenolytic bacteria such as Enterococcus faecalis predominate within the colon postoperatively, particularly at the site of the colon reconnection (i.e. anastomosis) in the early period of post-surgical recovery. The presence of collagenolytic bacteria at this site correlates with the tumor progression in a mouse model of post-surgical tumor development. In the present study we hypothesized, that collagenolytic bacteria, such as E. faecalis, play an important yet to be discovered role in tumor formation and progression. Therefore the aims of this study were to assess the role of collagenolytic E. faecalis on the migration and invasion of a murine colon cancer cell line. Results demonstrated that both migration and invasion were induced by E. faecalis with collagenolytic activity being required for only invasion. Bidirectional signaling in the E. faecalis-cancer cell interaction was observed by the discovering that the expression of gelE in E. faecalis, the gene required for collagenase production, is expressed in response to exposure to CT26 cells. The mechanism by which migration enhancement via E. faecalis occurs appears to be dependent on its ability to activate pro-uPA, a key element of the urokinase-plasminogen system, a pathway that is well – known to be important in cancer cell invasion and migration. Finally, we demonstrated that collagenase producing microbes preferentially colonize human colon cancer specimens.
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