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Extreme Dysbiosis of the Microbiome in Critical Illness. mSphere 2016; 1:mSphere00199-16. [PMID: 27602409 PMCID: PMC5007431 DOI: 10.1128/msphere.00199-16] [Citation(s) in RCA: 248] [Impact Index Per Article: 31.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2016] [Accepted: 08/06/2016] [Indexed: 01/21/2023] Open
Abstract
Critical illness may be associated with the loss of normal, “health promoting” bacteria, allowing overgrowth of disease-promoting pathogenic bacteria (dysbiosis), which, in turn, makes patients susceptible to hospital-acquired infections, sepsis, and organ failure. This has significant world health implications, because sepsis is becoming a leading cause of death worldwide, and hospital-acquired infections contribute to significant illness and increased costs. Thus, a trial that monitors the ICU patient microbiome to confirm and characterize this hypothesis is urgently needed. Our study analyzed the microbiomes of 115 critically ill subjects and demonstrated rapid dysbiosis from unexpected environmental sources after ICU admission. These data may provide the first steps toward defining targeted therapies that correct potentially “illness-promoting” dysbiosis with probiotics or with targeted, multimicrobe synthetic “stool pills” that restore a healthy microbiome in the ICU setting to improve patient outcomes. Critical illness is hypothesized to associate with loss of “health-promoting” commensal microbes and overgrowth of pathogenic bacteria (dysbiosis). This dysbiosis is believed to increase susceptibility to nosocomial infections, sepsis, and organ failure. A trial with prospective monitoring of the intensive care unit (ICU) patient microbiome using culture-independent techniques to confirm and characterize this dysbiosis is thus urgently needed. Characterizing ICU patient microbiome changes may provide first steps toward the development of diagnostic and therapeutic interventions using microbiome signatures. To characterize the ICU patient microbiome, we collected fecal, oral, and skin samples from 115 mixed ICU patients across four centers in the United States and Canada. Samples were collected at two time points: within 48 h of ICU admission, and at ICU discharge or on ICU day 10. Sample collection and processing were performed according to Earth Microbiome Project protocols. We applied SourceTracker to assess the source composition of ICU patient samples by using Qiita, including samples from the American Gut Project (AGP), mammalian corpse decomposition samples, childhood (Global Gut study), and house surfaces. Our results demonstrate that critical illness leads to significant and rapid dysbiosis. Many taxons significantly depleted from ICU patients versus AGP healthy controls are key “health-promoting” organisms, and overgrowth of known pathogens was frequent. Source compositions of ICU patient samples are largely uncharacteristic of the expected community type. Between time points and within a patient, the source composition changed dramatically. Our initial results show great promise for microbiome signatures as diagnostic markers and guides to therapeutic interventions in the ICU to repopulate the normal, “health-promoting” microbiome and thereby improve patient outcomes. IMPORTANCE Critical illness may be associated with the loss of normal, “health promoting” bacteria, allowing overgrowth of disease-promoting pathogenic bacteria (dysbiosis), which, in turn, makes patients susceptible to hospital-acquired infections, sepsis, and organ failure. This has significant world health implications, because sepsis is becoming a leading cause of death worldwide, and hospital-acquired infections contribute to significant illness and increased costs. Thus, a trial that monitors the ICU patient microbiome to confirm and characterize this hypothesis is urgently needed. Our study analyzed the microbiomes of 115 critically ill subjects and demonstrated rapid dysbiosis from unexpected environmental sources after ICU admission. These data may provide the first steps toward defining targeted therapies that correct potentially “illness-promoting” dysbiosis with probiotics or with targeted, multimicrobe synthetic “stool pills” that restore a healthy microbiome in the ICU setting to improve patient outcomes. Podcast: A podcast concerning this article is available.
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202
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Lankelma JM, Belzer C, Hoogendijk AJ, de Vos AF, de Vos WM, van der Poll T, Wiersinga WJ. Antibiotic-Induced Gut Microbiota Disruption Decreases TNF-α Release by Mononuclear Cells in Healthy Adults. Clin Transl Gastroenterol 2016; 7:e186. [PMID: 27489950 PMCID: PMC5543405 DOI: 10.1038/ctg.2016.43] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/10/2016] [Accepted: 07/01/2016] [Indexed: 02/06/2023] Open
Abstract
Objectives: Broad-spectrum antibiotics disrupt the intestinal microbiota. The microbiota is essential for physiological processes, such as the development of the gut immune system. Recent murine data suggest that the intestinal microbiota also modulates systemic innate immune responses; however, evidence in humans is lacking. Methods: Twelve healthy young men were given oral broad-spectrum antibiotics (ciprofloxacin 500 mg bid, vancomycin 500 mg tid and metronidazole 500 mg tid) for 7 days. At baseline, 1 day, and 6 weeks after antibiotics, blood and feces were sampled. Whole blood and isolated mononuclear cells were stimulated with selected Toll-like receptor agonists and heat-killed bacteria. Microbiota diversity and composition was determined using bacterial 16S rDNA sequencing. Results: One day after the antibiotic course, microbial diversity was significantly lower compared with baseline. After antibiotic therapy, systemic mononuclear cells produced lower levels of tumor necrosis factor (TNF)-α after ex vivo stimulation with lipopolysaccharide (LPS). This diminished capacity to produce TNF-α was restored 6 weeks after cessation of antibiotic therapy. In whole blood, a reduced capacity to release interleukin (IL)-1β and IL-6 was observed after LPS stimulation. Antibiotic treatment did not impact on differential leukocyte counts, phagocytosis, and cell surface markers of neutrophils and monocytes. Conclusions: In this proof-of-principle study of healthy subjects, microbiota disruption by broad-spectrum antibiotics is reversibly associated with decreased systemic cellular responsiveness towards LPS. The implications of these findings in a clinical setting remain to be determined.
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Affiliation(s)
- Jacqueline M Lankelma
- Center for Experimental and Molecular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Clara Belzer
- Laboratory of Microbiology, Wageningen University, Wageningen, The Netherlands
| | - Arie J Hoogendijk
- Center for Experimental and Molecular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Alex F de Vos
- Center for Experimental and Molecular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - Willem M de Vos
- Laboratory of Microbiology, Wageningen University, Wageningen, The Netherlands.,RPU Immunobiology, Department of Bacteriology and Immunology, Helsinki University, Helsinski, Finland
| | - Tom van der Poll
- Center for Experimental and Molecular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.,Department of Medicine, Division of Infectious Diseases, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
| | - W Joost Wiersinga
- Center for Experimental and Molecular Medicine, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands.,Department of Medicine, Division of Infectious Diseases, Academic Medical Center, University of Amsterdam, Amsterdam, The Netherlands
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203
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Dickson RP, Singer BH, Newstead MW, Falkowski NR, Erb-Downward JR, Standiford TJ, Huffnagle GB. Enrichment of the lung microbiome with gut bacteria in sepsis and the acute respiratory distress syndrome. Nat Microbiol 2016; 1:16113. [PMID: 27670109 DOI: 10.1038/nmicrobiol.2016.113] [Citation(s) in RCA: 400] [Impact Index Per Article: 50.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2016] [Accepted: 06/03/2016] [Indexed: 12/15/2022]
Abstract
Sepsis and the acute respiratory distress syndrome (ARDS) are major causes of mortality without targeted therapies. Although many experimental and clinical observations have implicated gut microbiota in the pathogenesis of these diseases, culture-based studies have failed to demonstrate translocation of bacteria to the lungs in critically ill patients. Here, we report culture-independent evidence that the lung microbiome is enriched with gut bacteria both in a murine model of sepsis and in humans with established ARDS. Following experimental sepsis, lung communities were dominated by viable gut-associated bacteria. Ecological analysis identified the lower gastrointestinal tract, rather than the upper respiratory tract, as the likely source community of post-sepsis lung bacteria. In bronchoalveolar lavage fluid from humans with ARDS, gut-specific bacteria (Bacteroides spp.) were common and abundant, undetected by culture and correlated with the intensity of systemic inflammation. Alveolar TNF-α, a key mediator of alveolar inflammation in ARDS, was significantly correlated with altered lung microbiota. Our results demonstrate that the lung microbiome is enriched with gut-associated bacteria in sepsis and ARDS, potentially representing a shared mechanism of pathogenesis in these common and lethal diseases.
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Affiliation(s)
- Robert P Dickson
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
| | - Benjamin H Singer
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
| | - Michael W Newstead
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
| | - Nicole R Falkowski
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
| | - John R Erb-Downward
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
| | - Theodore J Standiford
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
| | - Gary B Huffnagle
- Division of Pulmonary and Critical Care Medicine, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA.,Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109, USA
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204
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The interplay between microbiota and inflammation: lessons from peritonitis and sepsis. Clin Transl Immunology 2016; 5:e90. [PMID: 27525063 PMCID: PMC4973320 DOI: 10.1038/cti.2016.32] [Citation(s) in RCA: 26] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2016] [Revised: 04/13/2016] [Accepted: 04/14/2016] [Indexed: 12/22/2022] Open
Abstract
Mammals harbor a complex gut-associated microbiota, comprising bacteria that provide immunological, metabolic and neurological benefits to the host, and contribute to their well-being. However, dysregulation of the microbiota composition, known as dysbiosis, along with the associated mucosal immune response have a key role in the pathogenesis of many inflammatory diseases, including inflammatory bowel diseases (IBDs), type 1 and type 2 diabetes, asthma, multiple sclerosis, among others. In addition, outside the gut lumen, bacteria from microbiota are the causative agent of peritoneal inflammation, abdominal sepsis and systemic sepsis. Critical care interventions during sepsis by antibiotics induce dysbiosis and present acute and long-term poor prognosis. In this review, we discuss immunomodulatory effects of the microbial molecules and products, highlighting the role of Bacteroides fragilis, a human commensal with ambiguous interactions with the host. Moreover, we also address the impact of antibiotic treatment in sepsis outcome and discuss new insights for microbiota modulation.
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205
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Toward a Nuanced Understanding of the Role of Infection in Readmissions After Sepsis. Crit Care Med 2016; 44:634-5. [PMID: 26901548 DOI: 10.1097/ccm.0000000000001508] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
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206
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Conlan S, Park M, Deming C, Thomas PJ, Young AC, Coleman H, Sison C, Weingarten RA, Lau AF, Dekker JP, Palmore TN, Frank KM, Segre JA. Plasmid Dynamics in KPC-Positive Klebsiella pneumoniae during Long-Term Patient Colonization. mBio 2016; 7:e00742-16. [PMID: 27353756 PMCID: PMC4937214 DOI: 10.1128/mbio.00742-16] [Citation(s) in RCA: 87] [Impact Index Per Article: 10.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2016] [Accepted: 05/23/2016] [Indexed: 11/20/2022] Open
Abstract
UNLABELLED Carbapenem-resistant Klebsiella pneumoniae strains are formidable hospital pathogens that pose a serious threat to patients around the globe due to a rising incidence in health care facilities, high mortality rates associated with infection, and potential to spread antibiotic resistance to other bacterial species, such as Escherichia coli Over 6 months in 2011, 17 patients at the National Institutes of Health (NIH) Clinical Center became colonized with a highly virulent, transmissible carbapenem-resistant strain of K. pneumoniae Our real-time genomic sequencing tracked patient-to-patient routes of transmission and informed epidemiologists' actions to monitor and control this outbreak. Two of these patients remained colonized with carbapenemase-producing organisms for at least 2 to 4 years, providing the opportunity to undertake a focused genomic study of long-term colonization with antibiotic-resistant bacteria. Whole-genome sequencing studies shed light on the underlying complex microbial colonization, including mixed or evolving bacterial populations and gain or loss of plasmids. Isolates from NIH patient 15 showed complex plasmid rearrangements, leaving the chromosome and the blaKPC-carrying plasmid intact but rearranging the two other plasmids of this outbreak strain. NIH patient 16 has shown continuous colonization with blaKPC-positive organisms across multiple time points spanning 2011 to 2015. Genomic studies defined a complex pattern of succession and plasmid transmission across two different K. pneumoniae sequence types and an E. coli isolate. These findings demonstrate the utility of genomic methods for understanding strain succession, genome plasticity, and long-term carriage of antibiotic-resistant organisms. IMPORTANCE In 2011, the NIH Clinical Center had a nosocomial outbreak involving 19 patients who became colonized or infected with blaKPC-positive Klebsiella pneumoniae Patients who have intestinal colonization with blaKPC-positive K. pneumoniae are at risk for developing infections that are difficult or nearly impossible to treat with existing antibiotic options. Two of those patients remained colonized with blaKPC-positive Klebsiella pneumoniae for over a year, leading to the initiation of a detailed genomic analysis exploring mixed colonization, plasmid recombination, and plasmid diversification. Whole-genome sequence analysis identified a variety of changes, both subtle and large, in the blaKPC-positive organisms. Long-term colonization of patients with blaKPC-positive Klebsiella pneumoniae creates new opportunities for horizontal gene transfer of plasmids encoding antibiotic resistance genes and poses complications for the delivery of health care.
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Affiliation(s)
- Sean Conlan
- National Human Genome Research Institute, Bethesda, Maryland, USA
| | - Morgan Park
- National Institutes of Health Intramural Sequencing Center (NISC), Rockville, Maryland, USA
| | - Clayton Deming
- National Human Genome Research Institute, Bethesda, Maryland, USA
| | - Pamela J Thomas
- National Institutes of Health Intramural Sequencing Center (NISC), Rockville, Maryland, USA
| | - Alice C Young
- National Institutes of Health Intramural Sequencing Center (NISC), Rockville, Maryland, USA
| | - Holly Coleman
- National Institutes of Health Intramural Sequencing Center (NISC), Rockville, Maryland, USA
| | - Christina Sison
- National Institutes of Health Intramural Sequencing Center (NISC), Rockville, Maryland, USA
| | | | - Anna F Lau
- National Institutes of Health Clinical Center, Bethesda, Maryland, USA
| | - John P Dekker
- National Institutes of Health Clinical Center, Bethesda, Maryland, USA
| | - Tara N Palmore
- National Institutes of Health Clinical Center, Bethesda, Maryland, USA
| | - Karen M Frank
- National Institutes of Health Clinical Center, Bethesda, Maryland, USA
| | - Julia A Segre
- National Human Genome Research Institute, Bethesda, Maryland, USA
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207
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Krezalek MA, Skowron KB, Guyton KL, Shakhsheer B, Hyoju S, Alverdy JC. The intestinal microbiome and surgical disease. Curr Probl Surg 2016; 53:257-93. [PMID: 27497246 DOI: 10.1067/j.cpsurg.2016.06.001] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2016] [Accepted: 06/07/2016] [Indexed: 12/12/2022]
Affiliation(s)
- Monika A Krezalek
- Department of Surgery, Center for Surgical Infection Research and Therapeutics, Pritzker School of Medicine, University of Chicago, Chicago, IL
| | - Kinga B Skowron
- Department of Surgery, Center for Surgical Infection Research and Therapeutics, Pritzker School of Medicine, University of Chicago, Chicago, IL
| | - Kristina L Guyton
- Department of Surgery, Center for Surgical Infection Research and Therapeutics, Pritzker School of Medicine, University of Chicago, Chicago, IL
| | - Baddr Shakhsheer
- Department of Surgery, Center for Surgical Infection Research and Therapeutics, Pritzker School of Medicine, University of Chicago, Chicago, IL
| | - Sanjiv Hyoju
- Department of Surgery, Center for Surgical Infection Research and Therapeutics, Pritzker School of Medicine, University of Chicago, Chicago, IL
| | - John C Alverdy
- Department of Surgery, Center for Surgical Infection Research and Therapeutics, Pritzker School of Medicine, University of Chicago, Chicago, IL.
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208
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Dickstein Y, Edelman R, Dror T, Hussein K, Bar-Lavie Y, Paul M. Carbapenem-resistant Enterobacteriaceae colonization and infection in critically ill patients: a retrospective matched cohort comparison with non-carriers. J Hosp Infect 2016; 94:54-9. [PMID: 27392978 DOI: 10.1016/j.jhin.2016.05.018] [Citation(s) in RCA: 57] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2016] [Accepted: 05/31/2016] [Indexed: 11/28/2022]
Abstract
OBJECTIVES To examine whether carbapenem-resistant Enterobacteriaceae (CRE) carriage is associated with incidence of clinical infection as a means of assessing whether the morbidity and mortality associated with these bacteria are mediated by underlying conditions or intrinsic properties of CRE. METHODS This retrospective matched cohort study compared the incidence of invasive infections in CRE-colonized patients and matched non-carriers in the intensive care unit (ICU). The primary outcome was infection caused by CRE of the same species as the colonizing strain among CRE carriers, and infections caused by carbapenem-sensitive strains of the same organism in non-carriers. Hospital discharge and death were considered as competing events. Competing-risks hazard analysis was performed for the entire cohort and for a nested cohort matched by Acute Physiology and Chronic Health Evaluation (APACHE) II scores, stratified by matching. RESULTS In total, 146 CRE carriers were compared with 292 non-carriers. Patients were well matched for most risk factors for Enterobacteriaceae infection, including age, renal failure, previous invasive infection, previous hospitalization, APACHE II score, length of mechanical ventilation, length of hospitalization and CRE carriage. On regression analysis, colonization with CRE was independently associated with Enterobacteriaceae infection {cause-specific hazard ratio (CSHR) 2.06 [95% confidence interval (CI) 1.03-4.09]}. On regression analysis of the APACHE-II-matched cohort (N=284), colonization with CRE remained significantly associated with Enterobacteriaceae infection [CSHR 3.32 (95% CI 1.31-8.43)]. CONCLUSIONS Colonization with CRE was associated with at least a two-fold increased risk of infection by the colonizing strain amongst ICU patients.
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Affiliation(s)
- Y Dickstein
- Infectious Diseases Institute, Rambam Health Care Campus, Haifa, Israel; The Ruth and Bruce Rappaport Faculty of Medicine, Technion, Israel Institute of Technology, Haifa, Israel.
| | - R Edelman
- The Ruth and Bruce Rappaport Faculty of Medicine, Technion, Israel Institute of Technology, Haifa, Israel
| | - T Dror
- The Ruth and Bruce Rappaport Faculty of Medicine, Technion, Israel Institute of Technology, Haifa, Israel
| | - K Hussein
- Infectious Diseases Institute, Rambam Health Care Campus, Haifa, Israel; The Ruth and Bruce Rappaport Faculty of Medicine, Technion, Israel Institute of Technology, Haifa, Israel
| | - Y Bar-Lavie
- The Ruth and Bruce Rappaport Faculty of Medicine, Technion, Israel Institute of Technology, Haifa, Israel; Department of Intensive Care, Rambam Health Care Campus, Haifa, Israel
| | - M Paul
- Infectious Diseases Institute, Rambam Health Care Campus, Haifa, Israel; The Ruth and Bruce Rappaport Faculty of Medicine, Technion, Israel Institute of Technology, Haifa, Israel
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209
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Pettigrew MM, Johnson JK, Harris AD. The human microbiota: novel targets for hospital-acquired infections and antibiotic resistance. Ann Epidemiol 2016; 26:342-7. [PMID: 26994507 PMCID: PMC4892961 DOI: 10.1016/j.annepidem.2016.02.007] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Revised: 01/26/2016] [Accepted: 02/26/2016] [Indexed: 12/14/2022]
Abstract
PURPOSE Hospital-acquired infections are increasing in frequency due to multidrug resistant organisms (MDROs), and the spread of MDROs has eroded our ability to treat infections. Health care professionals cannot rely solely on traditional infection control measures and antimicrobial stewardship to prevent MDRO transmission. We review research on the microbiota as a target for infection control interventions. METHODS We performed a literature review of key research findings related to the microbiota as a target for infection control interventions. These data are summarized and used to outline challenges, opportunities, and unanswered questions in the field. RESULTS The healthy microbiota provides protective functions including colonization resistance, which refers to the microbiota's ability to prevent colonization and/or expansion of pathogens. Antibiotic use and other exposures in hospitalized patients are associated with disruptions of the microbiota that may reduce colonization resistance and select for antibiotic resistance. Novel methods to exploit protective mechanisms provided by an intact microbiota may provide the key to preventing the spread of MDROs in the health care setting. CONCLUSIONS Research on the microbiota as a target for infection control has been limited. Epidemiologic studies will facilitate progress toward the goal of manipulating the microbiota for control of MDROs in the health care setting.
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Affiliation(s)
- Melinda M Pettigrew
- Department of Epidemiology of Microbial Diseases, Yale School of Public Health, New Haven, CT.
| | - J Kristie Johnson
- Department of Pathology, University of Maryland School of Medicine, Baltimore, MD
| | - Anthony D Harris
- Department of Epidemiology, University of Maryland School of Medicine, Baltimore, MD
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210
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Shogan BD, Belogortseva N, Luong PM, Zaborin A, Lax S, Bethel C, Ward M, Muldoon JP, Singer M, An G, Umanskiy K, Konda V, Shakhsheer B, Luo J, Klabbers R, Hancock LE, Gilbert J, Zaborina O, Alverdy JC. Collagen degradation and MMP9 activation by Enterococcus faecalis contribute to intestinal anastomotic leak. Sci Transl Med 2016; 7:286ra68. [PMID: 25947163 DOI: 10.1126/scitranslmed.3010658] [Citation(s) in RCA: 256] [Impact Index Per Article: 32.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
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.
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Affiliation(s)
- Benjamin D Shogan
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | | | - Preston M Luong
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | - Alexander Zaborin
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | - Simon Lax
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | - Cindy Bethel
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | - Marc Ward
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | | | - Mark Singer
- NorthShore University HealthSystem, Evanston, IL 60201, USA
| | - Gary An
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | | | - Vani Konda
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | - Baddr Shakhsheer
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | - James Luo
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | - Robin Klabbers
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA. Department of Surgery, Radboud University Nijmegen Medical Centre, Nijmegen, Netherlands
| | | | - Jack Gilbert
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA. Argonne National Laboratory, Argonne, IL 60439, USA
| | - Olga Zaborina
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA
| | - John C Alverdy
- University of Chicago Pritzker School of Medicine, Chicago, IL 60637, USA.
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211
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Pseudomonas aeruginosa Colonization in the Intensive Care Unit: Prevalence, Risk Factors, and Clinical Outcomes. Infect Control Hosp Epidemiol 2016; 37:544-8. [PMID: 26832307 DOI: 10.1017/ice.2015.346] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
OBJECTIVE To determine the prevalence of Pseudomonas aeruginosa colonization on intensive care unit (ICU) admission, risk factors for P. aeruginosa colonization, and the incidence of subsequent clinical culture with P. aeruginosa among those colonized and not colonized. METHODS We conducted a cohort study of patients admitted to a medical or surgical intensive care unit of a tertiary care hospital. Patients had admission perirectal surveillance cultures performed. Risk factors analyzed included comorbidities at admission, age, sex, antibiotics received during current hospitalization before ICU admission, and type of ICU. RESULTS Of 1,840 patients, 213 (11.6%) were colonized with P. aeruginosa on ICU admission. Significant risk factors in the multivariable analysis for colonization were age (odds ratio, 1.02 [95% CI, 1.01-1.03]), anemia (1.90 [1.05-3.42]), and neurologic disorder (1.80 [1.27-2.54]). Of the 213 patients colonized with P. aeruginosa on admission, 41 (19.2%) had a subsequent clinical culture positive for P. aeruginosa on ICU admission and 60 (28.2%) had a subsequent clinical culture positive for P. aeruginosa in the current hospitalization (ICU period and post-ICU period). Of these 60 patients, 49 (81.7%) had clinical infections. Of the 1,627 patients not colonized on admission, only 68 (4.2%) had a subsequent clinical culture positive for P. aeruginosa in the current hospitalization. Patients colonized with P. aeruginosa were more likely to have a subsequent positive clinical culture than patients not colonized (incidence rate ratio, 6.74 [95% CI, 4.91-9.25]). CONCLUSIONS Prediction rules or rapid diagnostic testing will help clinicians more appropriately choose empirical antibiotic therapy for subsequent infections.
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212
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Zhang XY, Liu ZM, Zhang HF, Li YS, Wen SH, Shen JT, Huang WQ, Liu KX. TGF-β1 improves mucosal IgA dysfunction and dysbiosis following intestinal ischaemia-reperfusion in mice. J Cell Mol Med 2016; 20:1014-23. [PMID: 26820382 PMCID: PMC4882980 DOI: 10.1111/jcmm.12789] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Accepted: 12/13/2015] [Indexed: 12/14/2022] Open
Abstract
Intestinal ischaemia/reperfusion (I/R) severely disrupts gut barriers and leads to high mortality in the critical care setting. Transforming growth factor (TGF)-β1 plays a pivotal role in intestinal cellular and immune regulation. However, the effects of TGF-β1 on intestinal I/R injury remain unclear. Thus, we aimed to investigate the effects of TGF-β1 on gut barriers after intestinal I/R and the molecular mechanisms. Intestinal I/R model was produced in mice by clamping the superior mesenteric artery for 1 hr followed by reperfusion. Recombinant TGF-β1 was intravenously infused at 15 min. before ischaemia. The results showed that within 2 hrs after reperfusion, intestinal I/R disturbed intestinal immunoglobulin A class switch recombination (IgA CSR), the key process of mucosal IgA synthesis, and resulted in IgA dysfunction, as evidenced by decreased production and bacteria-binding capacity of IgA. Meanwhile, the disruptions of intestinal microflora and mucosal structure were exhibited. Transforming growth factor-β1 activated IgA CSR as evidenced by the increased activation molecules and IgA precursors. Strikingly, TGF-β1 improved intestinal mucosal IgA dysfunction, dysbiosis and epithelial damage at the early stage after reperfusion. In addition, SB-431542, a specific inhibitor of activating mothers against decapentaplegic homologue (SMAD) 2/3, totally blocked the inductive effect of TGF-β1 on IgA CSR and almost abrogated the above protective effects on intestinal barriers. Taken together, our study demonstrates that TGF-β1 protects intestinal mucosal IgA immunity, microbiota and epithelial integrity against I/R injury mainly through TGF-β receptor 1/SMAD 2/3 pathway. Induction of IgA CSR may be involved in the protection conferred by TGF-β1.
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Affiliation(s)
- Xu-Yu Zhang
- Department of Anesthesiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Zi-Meng Liu
- Surgical Intensive Care Unit, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Hu-Fei Zhang
- Department of Anesthesiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Yun-Sheng Li
- Department of Anesthesiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Shi-Hong Wen
- Department of Anesthesiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Jian-Tong Shen
- Department of Anesthesiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Wen-Qi Huang
- Department of Anesthesiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
| | - Ke-Xuan Liu
- Department of Anesthesiology, The First Affiliated Hospital, Sun Yat-sen University, Guangzhou, China
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213
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Gilbert JA, Alverdy J. Stool consistency as a major confounding factor affecting microbiota composition: an ignored variable? Gut 2016; 65:1-2. [PMID: 26187505 DOI: 10.1136/gutjnl-2015-310043] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/25/2015] [Accepted: 07/02/2015] [Indexed: 12/08/2022]
Affiliation(s)
- Jack A Gilbert
- Biosciences Division (BIO), Argonne National Laboratory, Argonne, Illinois, USA Department of Ecology & Evolution, University of Chicago, Chicago, Illinois, USA Department of Surgery, University of Chicago, Chicago, Illinois, USA Institute for Genomic and Systems Biology, University of Chicago, Chicago, Illinois, USA The Marine Biological Laboratory, Woods Hole, Massachusetts, USA
| | - John Alverdy
- Department of Surgery, University of Chicago, Chicago, Illinois, USA
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214
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Ojima M, Motooka D, Shimizu K, Gotoh K, Shintani A, Yoshiya K, Nakamura S, Ogura H, Iida T, Shimazu T. Metagenomic Analysis Reveals Dynamic Changes of Whole Gut Microbiota in the Acute Phase of Intensive Care Unit Patients. Dig Dis Sci 2016; 61:1628-34. [PMID: 26715502 PMCID: PMC4875048 DOI: 10.1007/s10620-015-4011-3] [Citation(s) in RCA: 130] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2015] [Accepted: 12/14/2015] [Indexed: 12/12/2022]
Abstract
BACKGROUND Metagenomic analysis targeting the 16S rRNA gene has made it possible to characterize the vast array of microorganisms contained in the gut. AIM The purpose of this study was to evaluate how gut microbiota change in intensive care unit (ICU) patients in the acute phase after admission. METHODS This prospective observational cohort study investigated 12 patients admitted to a single ICU of a large urban tertiary referral hospital. All patients were mechanically ventilated on admission. Fecal samples were collected from patients on days 1-2, 2-4, 5-8, and 7-10 after admission. DNA was extracted from fecal samples, and 16S rRNA deep sequencing was performed to monitor gut changes. RESULTS Bacteria belonging to the phyla Firmicutes or Bacteroidetes were predominant in each sample. We observed serial dynamic changes in the percentages of Bacteroidetes and Firmicutes that were significantly altered during study period (p < 0.05). A ratio of Bacteroidetes to Firmicutes (B/F ratio) of >10 was seen in four of the six patients who died, whereas a B/F ratio of <0.10 was seen in only one of the six deaths. None of the survivors had a B/F ratio of >10 or <0.10. There was a statistical difference in the B/F ratio between the dead patients and survivors (p = 0.022). CONCLUSIONS Dynamic changes in gut microbiota at the phylum level of ICU patients during the acute phase were identified by high-throughput DNA sequencing. An extreme imbalance in gut microbiota may be associated with prognosis in critically ill patients.
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Affiliation(s)
- Masahiro Ojima
- />Department of Traumatology and Acute Critical Medicine, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871 Japan
| | - Daisuke Motooka
- />Department of Infection Metagenomics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka Japan
| | - Kentaro Shimizu
- />Department of Traumatology and Acute Critical Medicine, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871 Japan
| | - Kazuyoshi Gotoh
- />Department of Infection Metagenomics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka Japan
| | - Ayumi Shintani
- />Department of Clinical Epidemiology and Biostatistics, Graduate School of Medicine, Osaka University, Suita, Osaka Japan
| | - Kazuhisa Yoshiya
- />Department of Traumatology and Acute Critical Medicine, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871 Japan
| | - Shota Nakamura
- />Department of Infection Metagenomics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka Japan
| | - Hiroshi Ogura
- />Department of Traumatology and Acute Critical Medicine, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871 Japan
| | - Tetsuya Iida
- />Department of Infection Metagenomics, Research Institute for Microbial Diseases, Osaka University, Suita, Osaka Japan
| | - Takeshi Shimazu
- />Department of Traumatology and Acute Critical Medicine, Osaka University Graduate School of Medicine, Suita, Osaka 565-0871 Japan
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215
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Dickson RP. The microbiome and critical illness. THE LANCET. RESPIRATORY MEDICINE 2016; 4:59-72. [PMID: 26700442 PMCID: PMC4752077 DOI: 10.1016/s2213-2600(15)00427-0] [Citation(s) in RCA: 280] [Impact Index Per Article: 35.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2015] [Revised: 10/10/2015] [Accepted: 10/13/2015] [Indexed: 12/12/2022]
Abstract
The central role of the microbiome in critical illness is supported by a half century of experimental and clinical study. The physiological effects of critical illness and the clinical interventions of intensive care substantially alter the microbiome. In turn, the microbiome predicts patients' susceptibility to disease, and manipulation of the microbiome has prevented or modulated critical illness in animal models and clinical trials. This Review surveys the microbial ecology of critically ill patients, presents the facts and unanswered questions surrounding gut-derived sepsis, and explores the radically altered ecosystem of the injured alveolus. The revolution in culture-independent microbiology has provided the tools needed to target the microbiome rationally for the prevention and treatment of critical illness, holding great promise to improve the acute and chronic outcomes of the critically ill.
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Affiliation(s)
- Robert P Dickson
- Department of Internal Medicine, Division of Pulmonary and Critical Care Medicine, University of Michigan Medical School, Ann Arbor, MI, USA.
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216
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Prescott HC, Dickson RP, Rogers MAM, Langa KM, Iwashyna TJ. Hospitalization Type and Subsequent Severe Sepsis. Am J Respir Crit Care Med 2015; 192:581-8. [PMID: 26016947 DOI: 10.1164/rccm.201503-0483oc] [Citation(s) in RCA: 114] [Impact Index Per Article: 12.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
RATIONALE Hospitalization is associated with microbiome perturbation (dysbiosis), and this perturbation is more severe in patients treated with antimicrobials. OBJECTIVES To evaluate whether hospitalizations known to be associated with periods of microbiome perturbation are associated with increased risk of severe sepsis after hospital discharge. METHODS We studied participants in the U.S. Health and Retirement Study with linked Medicare claims (1998-2010). We measured whether three hospitalization types associated with increasing severity of probable dysbiosis (non-infection-related hospitalization, infection-related hospitalization, and hospitalization with Clostridium difficile infection [CDI]) were associated with increasing risk for severe sepsis in the 90 days after hospital discharge. We used two study designs: the first was a longitudinal design with between-person comparisons and the second was a self-controlled case series design using within-person comparison. MEASUREMENTS AND MAIN RESULTS We identified 43,095 hospitalizations among 10,996 Health and Retirement Study-Medicare participants. In the 90 days following non-infection-related hospitalization, infection-related hospitalization, and hospitalization with CDI, adjusted probabilities of subsequent admission for severe sepsis were 4.1% (95% confidence interval [CI], 3.8-4.4%), 7.1% (95% CI, 6.6-7.6%), and 10.7% (95% CI, 7.7-13.8%), respectively. The incidence rate ratio (IRR) of severe sepsis was 3.3-fold greater during the 90 days after hospitalizations than during other observation periods. The IRR was 30% greater after an infection-related hospitalization versus a non-infection-related hospitalization. The IRR was 70% greater after a hospitalization with CDI than an infection-related hospitalization without CDI. CONCLUSIONS There is a strong dose-response relationship between events known to result in dysbiosis and subsequent severe sepsis hospitalization that is not present for rehospitalization for nonsepsis diagnoses.
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Affiliation(s)
- Hallie C Prescott
- 1 Department of Internal Medicine and.,2 Institute for Healthcare Policy and Innovation, University of Michigan, Ann Arbor, Michigan
| | | | - Mary A M Rogers
- 1 Department of Internal Medicine and.,2 Institute for Healthcare Policy and Innovation, University of Michigan, Ann Arbor, Michigan
| | - Kenneth M Langa
- 1 Department of Internal Medicine and.,2 Institute for Healthcare Policy and Innovation, University of Michigan, Ann Arbor, Michigan.,3 VA Center for Clinical Management Research, HSR&D Center of Innovation, Ann Arbor, Michigan; and.,4 Institute for Social Research, Ann Arbor, Michigan
| | - Theodore J Iwashyna
- 1 Department of Internal Medicine and.,2 Institute for Healthcare Policy and Innovation, University of Michigan, Ann Arbor, Michigan.,3 VA Center for Clinical Management Research, HSR&D Center of Innovation, Ann Arbor, Michigan; and.,4 Institute for Social Research, Ann Arbor, Michigan
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217
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Latorre M, Krishnareddy S, Freedberg DE. Microbiome as mediator: Do systemic infections start in the gut? World J Gastroenterol 2015; 21:10487-10492. [PMID: 26457009 PMCID: PMC4588071 DOI: 10.3748/wjg.v21.i37.10487] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/29/2015] [Revised: 04/28/2015] [Accepted: 08/31/2015] [Indexed: 02/06/2023] Open
Abstract
The intestinal microbiome is emerging as a crucial mediator between external insults and systemic infections. New research suggests that our intestinal microorganisms contribute to critical illness and the development of non-gastrointestinal infectious diseases. Common pathways include a loss of fecal intestinal bacterial diversity and a disproportionate increase in toxogenic bacterial species. Therapeutic interventions targeting the microbiome - primarily probiotics - have yielded limited results to date. However, knowledge in this area is rapidly expanding and microbiome-based therapy such as short-chain fatty acids may eventually become a standard strategy for preventing systemic infections in the context of critical illness.
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218
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Lax S, Nagler CR, Gilbert JA. Our interface with the built environment: immunity and the indoor microbiota. Trends Immunol 2015; 36:121-3. [PMID: 25754179 DOI: 10.1016/j.it.2015.01.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2014] [Revised: 01/05/2015] [Accepted: 01/07/2015] [Indexed: 12/18/2022]
Abstract
The rise of urbanization and an increasingly indoor lifestyle has affected human interactions with our microbiota in unprecedented ways. We discuss how this lifestyle may influence immune development and function, and argue that it is time that we examined ways to manipulate the indoor environment to increase our exposure to a wider phylogeny of microorganisms. An important step is to continue to engage citizen scientists in the efforts to characterize our interactions with the diverse microbial environments that we inhabit.
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Affiliation(s)
- Simon Lax
- Institute for Genomic and Systems Biology, Biosciences Department, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA; Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637, USA
| | - Cathryn R Nagler
- Committee on Immunology, Department of Pathology, University of Chicago, 924 East 57th Street, Chicago, IL 60637, USA
| | - Jack A Gilbert
- Institute for Genomic and Systems Biology, Biosciences Department, Argonne National Laboratory, 9700 South Cass Avenue, Argonne, IL 60439, USA; Department of Ecology and Evolution, University of Chicago, 1101 East 57th Street, Chicago, IL 60637, USA; Marine Biological Laboratory, 7 MBL Street, Woods Hole, MA 02543, USA; College of Environmental and Resource Sciences, Zhejiang University, Hangzhou, 310058, China.
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219
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Goldsmith JR, Sartor RB. Response to the letter by Brotherton regarding "insoluble fiber and intestinal microbiota metabolism". J Gastroenterol 2015; 50:492-3. [PMID: 25663612 DOI: 10.1007/s00535-015-1044-5] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/21/2015] [Accepted: 01/22/2015] [Indexed: 02/04/2023]
Affiliation(s)
- Jason R Goldsmith
- School of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, USA,
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220
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Brotherton CS. Insoluble fiber and intestinal microbiota metabolism. J Gastroenterol 2015; 50:491. [PMID: 25652234 DOI: 10.1007/s00535-015-1043-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/19/2014] [Accepted: 12/24/2014] [Indexed: 02/04/2023]
Affiliation(s)
- Carol S Brotherton
- School of Nursing, George Mason University, 4400 University Drive, MS 3C4, Fairfax, VA, 22030, USA,
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221
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Christley S, Cockrell C, An G. Computational Studies of the Intestinal Host-Microbiota Interactome. COMPUTATION (BASEL, SWITZERLAND) 2015; 3:2-28. [PMID: 34765258 PMCID: PMC8580329 DOI: 10.3390/computation3010002] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
A large and growing body of research implicates aberrant immune response and compositional shifts of the intestinal microbiota in the pathogenesis of many intestinal disorders. The molecular and physical interaction between the host and the microbiota, known as the host-microbiota interactome, is one of the key drivers in the pathophysiology of many of these disorders. This host-microbiota interactome is a set of dynamic and complex processes, and needs to be treated as a distinct entity and subject for study. Disentangling this complex web of interactions will require novel approaches, using a combination of data-driven bioinformatics with knowledge-driven computational modeling. This review describes the computational approaches for investigating the host-microbiota interactome, with emphasis on the human intestinal tract and innate immunity, and highlights open challenges and existing gaps in the computation methodology for advancing our knowledge about this important facet of human health.
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Affiliation(s)
- Scott Christley
- Department of Surgery, University of Chicago, 5841 South Maryland Avenue, Chicago, IL 60637, USA
| | - Chase Cockrell
- Department of Surgery, University of Chicago, 5841 South Maryland Avenue, Chicago, IL 60637, USA
| | - Gary An
- Department of Surgery, University of Chicago, 5841 South Maryland Avenue, Chicago, IL 60637, USA
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222
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Abstract
Since proof of the germ theory of disease in the late 19th century, a major focus of the fields of microbiology and infectious diseases has been to seek differences between pathogenic and nonpathogenic microbes and the role that the host plays in microbial pathogenesis. Remarkably, despite the increasing recognition that host immunity plays a role in microbial pathogenesis, there has been little discussion about what constitutes a host. Historically, hosts have been viewed in the context of their fitness or immunological status and characterized by adjectives such as immune, immunocompetent, immunosuppressed, immunocompromised, or immunologically impaired. However, in recent years it has become apparent that the microbiota has profound effects on host homeostasis and susceptibility to microbial diseases in addition to its effects on host immunity. This raises the question of how to incorporate the microbiota into defining a host. This definitional problem is further complicated because neither host nor microbial properties are adequate to predict the outcome of host-microbe interaction because this outcome exhibits emergent properties. In this essay, we revisit the damage-response framework (DRF) of microbial pathogenesis and demonstrate how it can incorporate the rapidly accumulating information being generated by the microbiome revolution. We use the tenets of the DRF to put forth the following definition of a host: a host is an entity that houses an associated microbiome/microbiota and interacts with microbes such that the outcome results in damage, benefit, or indifference, thus resulting in the states of symbiosis, colonization, commensalism, latency, and disease.
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