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The National Institutes of Health (NIH) organized a three-day human microbiome research workshop, August 16-18, 2017, to highlight the accomplishments of the 10-year Human Microbiome Project program, the outcomes of the investments made by the 21 NIH Institutes and Centers which now fund this area, and the technical challenges and knowledge gaps which will need to be addressed in order for this field to advance over the next 10 years. This report summarizes the key points in the talks, round table discussions, and Joint Agency Panel from this workshop.

Background:The microbiome influences malaria parasite fitness and transmission efficiency in mosquitoes and appears to affect malaria dynamics in mammalian hosts as well. Nascent research examining the interrelationship of malaria and the mammalian microbiome has yielded interesting insights inviting further study. Methods:We conducted a systematic review of the literature examining associations between the microbiome and malaria in mammalian hosts. An electronic search algorithm was adapted to PubMed, MEDLINE, Scopus, Embase, and Web of Science, and reference lists of relevant sources were manually searched. Identified studies were screened and assessed independently by 2 authors, and results were compiled in a qualitative synthesis of the evidence. Results:Ten relevant studies were identified. They demonstrate associations between certain intestinal communities and protection against Plasmodium infection and modulation of disease severity. Plasmodium infection acutely and reversibly reshapes gut microbial composition in mice. The makeup of human skin microbial communities may influence mosquito attraction and thus disease transmission. Conclusions:Early research supports a relationship between malaria and the microbiome. The evidence is incomplete, but the observed associations are evocative and signal a promising avenue of inquiry. Microbiome-based studies of malaria can be readily integrated into field-based research.

The risk of colorectal cancer [CRC] is increased in patients with inflammatory bowel disease [IBD], particularly in extensive ulcerative colitis [UC] and Crohn's colitis. Gut microbiota have been implicated in the pathogenesis of CRC via multiple mechanisms, including the release of reactive oxygen species and genotoxins, and induction of inflammation, as well as activation of the immune response. Gut microbiota can enhance their carcinogenic and proinflammatory properties by organising into biofilms, potentially making them more resistant to the host's immune system and to antibiotics. Colonic biofilms have the capacity to invade colonic tissue and accelerate tumorigenesis in tumour-prone models of mice. In the context of IBD, the prevalence of biofilms has been estimated to be up to 95%. Although the relationship between chronic inflammation and molecular mediators that contribute to IBD-associated CRC is well established, the role of gut microbiota and biofilms in this sequence is not fully understood. Because CRC can still arise in the absence of histological inflammation, there is a growing interest in identifying chemopreventive agents against IBD-associated CRC. Commonly used in the treatment of UC, 5-aminosalicylates have antimicrobial and anticarcinogenic properties that might have a role in the chemoprevention of CRC via the inhibition or modulation of carcinogenic gut microbiota and potentially of biofilm formation. Whether biologics and other IBD-targeted therapies can decrease the progression towards dysplasia and CRC, via mechanisms independent of inflammation, is still unknown. Further research is warranted to identify potential new microbial targets in therapy for chemoprevention of dysplasia and CRC in IBD. [ABSTRACT FROM AUTHOR]

Pro-carcinogenic bacteria have the potential to initiate and/or promote colon cancer, in part via immune mechanisms that are incompletely understood. Using ApcMin mice colonized with the human pathobiont enterotoxigenic Bacteroides fragilis (ETBF) as a model of microbe-induced colon tumorigenesis, we show that the Bacteroides fragilis toxin (BFT) triggers a pro-carcinogenic, multi-step inflammatory cascade requiring IL-17R, NF-κB, and Stat3 signaling in colonic epithelial cells (CECs). Although necessary, Stat3 activation in CECs is not sufficient to trigger ETBF colon tumorigenesis. Notably, IL-17-dependent NF-κB activation in CECs induces a proximal to distal mucosal gradient of C-X-C chemokines, including CXCL1, that mediates the recruitment of CXCR2-expressing polymorphonuclear immature myeloid cells with parallel onset of ETBF-mediated distal colon tumorigenesis. Thus, BFT induces a pro-carcinogenic signaling relay from the CEC to a mucosal Th17 response that results in selective NF-κB activation in distal colon CECs, which collectively triggers myeloid-cell-dependent distal colon tumorigenesis.

Recent evidence has shown a complex relationship between the gut microbiota, dietary nutrients, and cardiovascular disease (CVD). Trimethylamine-N-oxide (TMAO) production, initiated by the microbiota, has been associated with CVD events. We sought to test if this association exists in HIV-infected persons. After adjusting for aspirin use and CVD risk factors, HIV-infected men were more likely to have coronary stenosis in the second and third TMAO quartiles compared with the first quartile, but did not differ significantly in the fourth quartile. We found an inverted U-shaped association between TMAO levels and the presence of coronary artery stenosis among HIV-infected men.

Bacterial biofilms in the colon alter the host tissue microenvironment. A role for biofilms in colon cancer metabolism has been suggested but to date has not been evaluated. Using metabolomics, we investigated the metabolic influence that microbial biofilms have on colon tissues and the related occurrence of cancer. Patient-matched colon cancers and histologically normal tissues, with or without biofilms, were examined. We show the upregulation of polyamine metabolites in tissues from cancer hosts with significant enhancement of N(1), N(12)-diacetylspermine in both biofilm-positive cancer and normal tissues. Antibiotic treatment, which cleared biofilms, decreased N(1), N(12)-diacetylspermine levels to those seen in biofilm-negative tissues, indicating that host cancer and bacterial biofilm structures contribute to the polyamine metabolite pool. These results show that colonic mucosal biofilms alter the cancer metabolome to produce a regulator of cellular proliferation and colon cancer growth potentially affecting cancer development and progression.

Next-generation sequencing (NGS) technology has advanced our understanding of the human microbiome by allowing for the discovery and characterization of unculturable microbes with prediction of their function. Key NGS methods include 16S rRNA gene sequencing, shotgun metagenomic sequencing, and RNA sequencing. The choice of which NGS methodology to pursue for a given purpose is often unclear for clinicians and researchers. In this Review, we describe the fundamentals of NGS, with a focus on 16S rRNA and shotgun metagenomic sequencing. We also discuss pros and cons of each methodology as well as important concepts in data variability, study design, and clinical metadata collection. We further present examples of how NGS studies of the human microbiome have advanced our understanding of human disease pathophysiology across diverse clinical contexts, including the development of diagnostics and therapeutics. Finally, we share insights as to how NGS might further be integrated into and advance microbiome research and clinical care in the coming years., Introduction The number of microbial cells that reside on and in us rivals the number of our own cells (1). In health, we, the host, and microbes live in symbiosis. [...]

Mucus-invasive bacterial biofilms are identified on the colon mucosa of approximately 50% of colorectal cancer (CRC) patients and approximately 13% of healthy subjects. Here, we test the hypothesis that human colon biofilms comprise microbial communities that are carcinogenic in CRC mouse models. Homogenates of human biofilm-positive colon mucosa were prepared from tumor patients (tumor and paired normal tissues from surgical resections) or biofilm-positive biopsies from healthy individuals undergoing screening colonoscopy; homogenates of biofilm-negative colon biopsies from healthy individuals undergoing screening colonoscopy served as controls. After 12 weeks, biofilm-positive, but not biofilm-negative, human colon mucosal homogenates induced colon tumor formation in 3 mouse colon tumor models (germ-free [Apc.sup.Min[DELTA]850/+]; [Il10.sup.-/-] or [Apc.sup.Min[DELTA]850/+] and specific pathogen-free [Apc.sup.Min[DELTA]716/+] mice). Remarkably, biofilm-positive communities from healthy colonoscopy biopsies induced colon inflammation and tumors similarly to biofilm-positive tumor tissues. By 1 week, biofilm-positive human tumor homogenates, but not healthy biopsies, displayed consistent bacterial mucus invasion and biofilm formation in mouse colons. 16S rRNA gene sequencing and RNA-Seq analyses identified compositional and functional microbiota differences between mice colonized with biofilm-positive and biofilm-negative communities. These results suggest human colon mucosal biofilms, whether from tumor hosts or healthy individuals undergoing screening colonoscopy, are carcinogenic in murine models of CRC., Introduction The intestinal microbiome has been implicated in a wide variety of diseases, spanning from metabolic, neurologic, and cardiovascular conditions to localized intestinal diseases, including colorectal cancer (CRC). In recent [...]