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Oles RE, Terrazas MC, Loomis LR, Neal MJ, Paulchakrabarti M, Zuffa S, Hsu CY, Vasquez Ayala A, Lee MH, Tribelhorn C, Belda-Ferre P, Bryant M, Zemlin J, Young J, Dulai P, Sandborn WJ, Sivagnanam M, Raffatellu M, Pride D, Dorrestein PC, Zengler K, Choudhury B, Knight R, Chu H. Pathogenic Bacteroides fragilis strains can emerge from gut-resident commensals. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.06.19.599758. [PMID: 38948766 PMCID: PMC11213024 DOI: 10.1101/2024.06.19.599758] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 07/02/2024]
Abstract
Bacteroides fragilis is a prominent member of the human gut microbiota, playing crucial roles in maintaining gut homeostasis and host health. Although it primarily functions as a beneficial commensal, B. fragilis can become pathogenic. To determine the genetic basis of its duality, we conducted a comparative genomic analysis of 813 B. fragilis strains, representing both commensal and pathogenic origins. Our findings reveal that pathogenic strains emerge across diverse phylogenetic lineages, due in part to rapid gene exchange and the adaptability of the accessory genome. We identified 16 phylogenetic groups, differentiated by genes associated with capsule composition, interspecies competition, and host interactions. A microbial genome-wide association study identified 44 genes linked to extra-intestinal survival and pathogenicity. These findings reveal how genomic diversity within commensal species can lead to the emergence of pathogenic traits, broadening our understanding of microbial evolution in the gut.
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Affiliation(s)
- Renee E. Oles
- Department of Pathology, University of California, San Diego, La Jolla, CA
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, CA
| | | | - Luke R. Loomis
- Department of Pathology, University of California, San Diego, La Jolla, CA
| | - Maxwell J. Neal
- Department of Bioengineering, University of California, San Diego, La Jolla, CA
| | | | - Simone Zuffa
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla
- Collaborative Mass Spectrometry Innovation Center, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA
| | - Chia-Yun Hsu
- Department of Pathology, University of California, San Diego, La Jolla, CA
| | | | - Michael H. Lee
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, CA
| | - Caitlin Tribelhorn
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, CA
| | - Pedro Belda-Ferre
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, CA
| | - MacKenzie Bryant
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, CA
| | - Jasmine Zemlin
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla
- Collaborative Mass Spectrometry Innovation Center, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA
| | - Jocelyn Young
- Division of Gastroenterology, Hepatology and Nutrition, University of California, San Diego and Rady Children’s Hospital, San Diego, CA
| | - Parambir Dulai
- Division of Gastroenterology, University of California, San Diego, La Jolla, CA
- Division of Gastroenterology, Northwestern University, Chicago, Illinois
| | - William J. Sandborn
- Division of Gastroenterology, University of California, San Diego, La Jolla, CA
- Center for Microbiome Innovation, University of California, San Diego, La Jolla, CA
| | - Mamata Sivagnanam
- Division of Gastroenterology, Hepatology and Nutrition, University of California, San Diego and Rady Children’s Hospital, San Diego, CA
| | - Manuela Raffatellu
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, CA
- Center for Microbiome Innovation, University of California, San Diego, La Jolla, CA
- Chiba University-UC San Diego Center for Mucosal Immunology, Allergy and Vaccines (cMAV), University of California, San Diego, La Jolla, CA
| | - David Pride
- Department of Pathology, University of California, San Diego, La Jolla, CA
- Center for Microbiome Innovation, University of California, San Diego, La Jolla, CA
- Center for Innovative Phage Applications and Therapeutics (IPATH), University of California, San Diego, La Jolla, CA
- Center of Advanced Laboratory Medicine (CALM), University of California, San Diego, La Jolla, CA
| | - Pieter C. Dorrestein
- Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla
- Collaborative Mass Spectrometry Innovation Center, Skaggs School of Pharmacy and Pharmaceutical Sciences, University of California, San Diego, La Jolla, CA
| | - Karsten Zengler
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, CA
- Department of Bioengineering, University of California, San Diego, La Jolla, CA
- Center for Microbiome Innovation, University of California, San Diego, La Jolla, CA
- Program in Materials Science and Engineering, University of California, San Diego, La Jolla, CA
| | - Biswa Choudhury
- GlycoAnalytics Core, University of California San Diego, San Diego, CA
| | - Rob Knight
- Division of Host-Microbe Systems and Therapeutics, Department of Pediatrics, University of California, San Diego, La Jolla, CA
- Center for Microbiome Innovation, University of California, San Diego, La Jolla, CA
- Shu Chien-Gene Lay Department of Bioengineering, University of California San Diego, La Jolla, CA
- Department of Computer Science & Engineering, University of California, San Diego, La Jolla, CA
- Halıcıoğlu Data Science Institute, University of California, San Diego, La Jolla, CA
| | - Hiutung Chu
- Department of Pathology, University of California, San Diego, La Jolla, CA
- Center for Microbiome Innovation, University of California, San Diego, La Jolla, CA
- Chiba University-UC San Diego Center for Mucosal Immunology, Allergy and Vaccines (cMAV), University of California, San Diego, La Jolla, CA
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Huang Y, Cao J, Zhu M, Wang Z, Jin Z, Xiong Z. Bacteroides fragilis aggravates high-fat diet-induced non-alcoholic fatty liver disease by regulating lipid metabolism and remodeling gut microbiota. Microbiol Spectr 2024; 12:e0339323. [PMID: 38411057 PMCID: PMC10986510 DOI: 10.1128/spectrum.03393-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2023] [Accepted: 02/05/2024] [Indexed: 02/28/2024] Open
Abstract
Gut microbiota dysbiosis is a prominent determinant that significantly contributes to the disruption of lipid metabolism. Consequently, it is essential to the occurrence and development of non-alcoholic fatty liver disease (NAFLD). Nevertheless, the connection between diet and symbiotic gut microbiota in the progression of NAFLD remains uncertain. The purpose of this study was to explore the role of supplementing commensal Bacteroides fragilis (B. fragilis) on lipid metabolism, gut microbiota, and metabolites in high-fat diet (HFD)-fed mice, elucidating the impact of gut microbiota and metabolites on the development of NAFLD. Our study revealed that supplementation with B. fragilis exacerbated both weight gain and obesity in mice. B. fragilis exacerbated blood glucose levels and liver dysfunction in mice. Furthermore, an increase in liver lipid accumulation and the upregulation of genes correlated with lipid metabolism were observed in mice. Under an HFD, supplementation of commensal B. fragilis resulted in alterations in the gut microbiota, notably a significant increase in Desulfovibrionaceae, which led to elevated endotoxin levels and thereby influenced the progression of NAFLD. It was interesting that the simultaneous examination of gut microbiota metabolites revealed a more pronounced impact of diet on short-chain fatty acids. This study represented the pioneering investigation into the impact of B. fragilis on NAFLD. Our findings demonstrated that B. fragilis induced dysregulation in the intestinal microbiota, leading to elevated levels of lipopolysaccharide and dysfunction in glucose and lipid metabolism, thereby exacerbating NAFLD.IMPORTANCESome intestinal symbiotic microbes are involved in the occurrence of the metabolic disorders. Our study investigated the impact of supplementing commensal Bacteroides fragilis on host metabolism in high-fat diet-fed mice. Research results indicated that adding a specific bacterial strain to the complex intestinal microecology can worsen metabolic conditions. This effect mainly affects the structural diversity of intestinal microorganisms, the increase in harmful bacteria in the gut, and the elevation of endotoxin levels, blood glucose, and lipid metabolism, thereby impacting the progression of non-alcoholic fatty liver disease (NAFLD). Understanding the principles that govern the establishment of microbial communities comprising multiple species is crucial for preventing or repairing dysfunctions in these communities, thereby enhancing host health and facilitating disease treatment. This study demonstrated that gut microbiota dysbiosis could contribute to metabolic dysfunction and provides new insights into how to promote gut microbiota in the prevention and therapy of NAFLD.
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Affiliation(s)
- Yumei Huang
- Department of Gastroenterology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Jiali Cao
- Department of Gastroenterology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Mengpei Zhu
- Department of Gastroenterology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Ziwen Wang
- Department of Gastroenterology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Ze Jin
- Department of Gastroenterology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
| | - Zhifan Xiong
- Department of Gastroenterology, Liyuan Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, Hubei, China
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Spigaglia P, Barbanti F, Germinario EAP, Criscuolo EM, Bruno G, Sanchez-Mete L, Porowska B, Stigliano V, Accarpio F, Oddi A, Zingale I, Rossi S, De Angelis R, Fabbri A. Comparison of microbiological profile of enterotoxigenic Bacteroides fragilis (ETBF) isolates from subjects with colorectal cancer (CRC) or intestinal pre-cancerous lesions versus healthy individuals and evaluation of environmental factors involved in intestinal dysbiosis. Anaerobe 2023; 82:102757. [PMID: 37380012 DOI: 10.1016/j.anaerobe.2023.102757] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2023] [Revised: 06/14/2023] [Accepted: 06/20/2023] [Indexed: 06/30/2023]
Abstract
OBJECTIVE The aim of this study was to analyze enterotoxigenic Bacteroides fragilis (ETBF) isolates from colorectal biopsies of subjects with a histological analysis positive for colorectal cancer (CRC), pre-cancerous lesions (pre-CRC) or with a healthy intestinal tissue and to evaluate the environmental factors that may not only concur to CRC development but may also affect gut microbiota composition. METHODS ETBF isolates were typed using the ERIC-PCR method, while PCR assays were performed to investigate the bft alleles, the B. fragilis pathogenicity island (BFPAI) region and the cepA, cfiA and cfxA genes. Susceptibility to antibiotics was tested using the agar dilution method. Environmental factors that could play a role in promoting intestinal dysbiosis were evaluated throughout a questionnaire administered to the subjects enrolled. RESULTS Six different ERIC-PCR types were identified. The type denominated C in this study was the most prevalent, in particular among the biopsies of subjects with pre-CRC, while an isolate belonging to a different type, denominated F, was detected in a biopsy from a subject with CRC. All the ETBF isolates from pre-CRC or CRC subjects had a B. fragilis pathogenicity island (BFPAI) region pattern I, while those from healthy individuals showed also different patterns. Furthermore, 71% of isolates from subjects with pre-CRC or CRC were resistant to two or more classes of antibiotics vs 43% of isolates from healthy individuals. The B. fragilis toxin BFT1 was the most frequently detected in this study, confirming the constant circulation of this isoform strains in Italy. Interestingly, BFT1 was found in 86% of the ETBF isolates from patients with CRC or pre-CRC, while the BFT2 was prevalent among the ETBF isolates from healthy subjects. No substantial differences based on sex, age, tobacco and alcohol consumption were observed between healthy and non-healthy individuals included in this study, while most of the subjects with CRC or pre-CRC lesions were subjected to pharmacological therapy (71%) and showed a body mass index (BMI) that falls within the overweight range (86%). CONCLUSIONS Our data suggest that some types of ETBF seem to better adapt and colonize the human gut and that the selective pressure exerted by factors related to lifestyle, such as pharmacological therapy and weight, could facilitate their persistence in the gut and their possible involvement in CRC development.
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Affiliation(s)
- Patrizia Spigaglia
- Department of Infectious Diseases, Istituto Superiore di Sanità, 00161, Rome, Italy.
| | - Fabrizio Barbanti
- Department of Infectious Diseases, Istituto Superiore di Sanità, 00161, Rome, Italy.
| | - Elena Angela Pia Germinario
- Department of Cardiovascular, Endocrine-Metabolic Diseases and Ageing, Istituto Superiore di Sanità, 00161, Rome, Italy.
| | | | - Giovanni Bruno
- Department of Translational and Precision Medicine, Gastroenterology Unit, Policlinic Umberto I, University of Rome 'Sapienza', 00161, Rome, Italy.
| | - Lupe Sanchez-Mete
- Gastroenterology and Digestive Endoscopy IRCCS Regina Elena National Cancer Institute, 00144, Rome, Italy.
| | - Barbara Porowska
- Digestive Endoscopy UOC CSC03 of the Department of General Surgery, Surgical Specialities "Paride Stefanini", Policlinic Umberto I, University of Rome 'Sapienza', 00161, Rome, Italy.
| | - Vittoria Stigliano
- Gastroenterology and Digestive Endoscopy IRCCS Regina Elena National Cancer Institute, 00144, Rome, Italy.
| | - Fabio Accarpio
- Digestive Endoscopy UOC CSC03 of the Department of General Surgery, Surgical Specialities "Paride Stefanini", Policlinic Umberto I, University of Rome 'Sapienza', 00161, Rome, Italy.
| | - Andrea Oddi
- Hepatopancreatobiliary Surgery, IRCCS Regina Elena National Cancer Institute, 00114, Rome, Italy.
| | - Ilaria Zingale
- Digestive Endoscopy UOC CSC03 of the Department of General Surgery, Surgical Specialities "Paride Stefanini", Policlinic Umberto I, University of Rome 'Sapienza', 00161, Rome, Italy.
| | - Silvia Rossi
- Department of Oncology and Molecular Medicine, Istituto Superiore di Sanità, 00161, Rome, Italy.
| | - Roberta De Angelis
- Department of Oncology and Molecular Medicine, Istituto Superiore di Sanità, 00161, Rome, Italy.
| | - Alessia Fabbri
- Department of Cardiovascular, Endocrine-Metabolic Diseases and Ageing, Istituto Superiore di Sanità, 00161, Rome, Italy.
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Scott N, Whittle E, Jeraldo P, Chia N. A systemic review of the role of enterotoxic Bacteroides fragilis in colorectal cancer. Neoplasia 2022; 29:100797. [PMID: 35461079 PMCID: PMC9046963 DOI: 10.1016/j.neo.2022.100797] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 03/25/2022] [Accepted: 04/01/2022] [Indexed: 12/13/2022]
Abstract
Enterotoxigenic Bacteroides fragilis (ETBF) has received significant attention for a possible association with, or causal role in, colorectal cancer (CRC). The goal of this review was to assess the status of the published evidence supporting (i) the association between ETBF and CRC and (ii) the causal role of ETBF in CRC. PubMed and Scopus searches were performed in August 2021 to identify human, animal, and cell studies pertaining to the role of ETBF in CRC. Inclusion criteria included the use of cell lines, mice, exposure to BFT or ETBF, and detection of bft. Review studies were excluded, and studies were limited to the English language. Quality of study design and risk of bias analysis was performed on the cell, animal, and human studies using ToxRTools, SYRCLE, and NOS, respectively. Ninety-five eligible studies were identified, this included 22 human studies, 24 animal studies, 43 cell studies, and 6 studies that included both cells and mice studies. We found that a large majority of studies supported an association or causal role of ETBF in CRC, as well as high levels of study bias was detected in the in vitro and in vivo studies. The high-level heterogeneity in study design and reporting made it difficult to synthesize these findings into a unified conclusion, suggesting that the need for future studies that include improved mechanistic models, longitudinal in vitro and in vivo evidence, and appropriate control of confounding factors will be required to confirm whether ETBF has a direct role in CRC etiopathogenesis.
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Affiliation(s)
- Nancy Scott
- Bioinformatics and Computational Biology, University of Minnesota, 111 South Broadway, Rochester, MN 55904, USA
| | - Emma Whittle
- Department of Surgery, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA
| | - Patricio Jeraldo
- Department of Surgery, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA; Microbiome Program, Center for Individualized Medicine, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA
| | - Nicholas Chia
- Department of Surgery, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA; Microbiome Program, Center for Individualized Medicine, Mayo Clinic, 200 First St. SW, Rochester, MN 55905, USA.
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5
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Patterson L, Allen J, Posey I, Shaw JJP, Costa-Pinheiro P, Walker SJ, Gademsey A, Wu X, Wu S, Zachos NC, Fox TE, Sears CL, Kester M. Glucosylceramide production maintains colon integrity in response to Bacteroides fragilis toxin-induced colon epithelial cell signaling. FASEB J 2020; 34:15922-15945. [PMID: 33047400 DOI: 10.1096/fj.202001669r] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 09/09/2020] [Accepted: 09/18/2020] [Indexed: 01/01/2023]
Abstract
Enterotoxigenic Bacteroides fragilis (ETBF) is a commensal bacterium of great importance to human health due to its ability to induce colitis and cause colon tumor formation in mice through the production of B. fragilis toxin (BFT). The formation of tumors is dependent on a pro-inflammatory signaling cascade, which begins with the disruption of epithelial barrier integrity through cleavage of E-cadherin. Here, we show that BFT increases levels of glucosylceramide, a vital intestinal sphingolipid, both in mice and in colon organoids (colonoids) generated from the distal colons of mice. When colonoids are treated with BFT in the presence of an inhibitor of glucosylceramide synthase (GCS), the enzyme responsible for generating glucosylceramide, colonoids become highly permeable, lose structural integrity, and eventually burst, releasing their contents into the extracellular matrix. By increasing glucosylceramide levels in colonoids via an inhibitor of glucocerebrosidase (GBA, the enzyme that degrades glucosylceramide), colonoid permeability was reduced, and bursting was significantly decreased. In the presence of BFT, pharmacological inhibition of GCS caused levels of tight junction protein 1 (TJP1) to decrease. However, when GBA was inhibited, TJP1 levels remained stable, suggesting that BFT-induced production of glucosylceramide helps to stabilize tight junctions. Taken together, our data demonstrate a glucosylceramide-dependent mechanism by which the colon epithelium responds to BFT.
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Affiliation(s)
- Logan Patterson
- Department of Pathology, University of Virginia, Charlottesville, VA, USA
| | - Jawara Allen
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Isabella Posey
- Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA
| | | | | | - Susan J Walker
- Department of Pharmacology, University of Virginia, Charlottesville, VA, USA
| | - Alexis Gademsey
- Department of Pharmacology, University of Virginia, Charlottesville, VA, USA
| | - Xinqun Wu
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Shaoguang Wu
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Nicholas C Zachos
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Todd E Fox
- Department of Pharmacology, University of Virginia, Charlottesville, VA, USA
| | - Cynthia L Sears
- Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Mark Kester
- Department of Pharmacology, University of Virginia, Charlottesville, VA, USA
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6
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Yekani M, Baghi HB, Naghili B, Vahed SZ, Sóki J, Memar MY. To resist and persist: Important factors in the pathogenesis of Bacteroides fragilis. Microb Pathog 2020; 149:104506. [PMID: 32950639 DOI: 10.1016/j.micpath.2020.104506] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2020] [Revised: 07/15/2020] [Accepted: 09/15/2020] [Indexed: 02/07/2023]
Abstract
Bacteroides fragilis is a most frequent anaerobic pathogen isolated from human infections, particularly found in the abdominal cavity. Different factors contribute to the pathogenesis and persistence of B. fragilis at infection sites. The knowledge of the virulence factors can provide applicable information for finding alternative options for the antibiotic therapy and treatment of B. fragilis caused infections. Herein, a comprehensive review of the important B. fragilis virulence factors was prepared. In addition to B. fragilis toxin (BFT) and its potential role in the diarrhea and cancer development, some other important virulence factors and characteristics of B. fragilis are described including capsular polysaccharides, iron acquisition, resistance to antimicrobial agents, and survival during the prolonged oxidative stress, quorum sensing, and secretion systems.
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Affiliation(s)
- Mina Yekani
- Department of Microbiology, Faculty of Medicine, Kashan University of Medical Sciences, Kashan, Iran; Student Research Committee,Kashan University of Medical Sciences, Kashan, Iran
| | - Hossein Bannazadeh Baghi
- Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; Immunology Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Behrooz Naghili
- Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
| | | | - József Sóki
- Institute of Clinical Microbiology, Faculty of Medicine, University of Szeged, Szeged, Hungary.
| | - Mohammad Yousef Memar
- Infectious and Tropical Diseases Research Center, Tabriz University of Medical Sciences, Tabriz, Iran; Microbiology Department, School of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran; Students' Research Committee, Tabriz University of Medical Sciences, Tabriz, Iran.
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7
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Valguarnera E, Wardenburg JB. Good Gone Bad: One Toxin Away From Disease for Bacteroides fragilis. J Mol Biol 2019; 432:765-785. [PMID: 31857085 DOI: 10.1016/j.jmb.2019.12.003] [Citation(s) in RCA: 54] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2019] [Revised: 11/27/2019] [Accepted: 12/05/2019] [Indexed: 02/06/2023]
Abstract
The human gut is colonized by hundreds of trillions of microorganisms whose acquisition begins during early infancy. Species from the Bacteroides genus are ubiquitous commensals, comprising about thirty percent of the human gut microbiota. Bacteroides fragilis is one of the least abundant Bacteroides species, yet is the most common anaerobe isolated from extraintestinal infections in humans. A subset of B. fragilis strains carry a genetic element that encodes a metalloprotease enterotoxin named Bacteroides fragilis toxin, or BFT. Toxin-bearing strains, or Enterotoxigenic B. fragilis (ETBF) cause acute and chronic intestinal disease in children and adults. Despite this association with disease, around twenty percent of the human population appear to be asymptomatic carriers of ETBF. BFT damages the colonic epithelial barrier by inducing cleavage of the zonula adherens protein E-cadherin and initiating a cell signaling response characterized by inflammation and c-Myc-dependent pro-oncogenic hyperproliferation. As a consequence, mice harboring genetic mutations that predispose to colonic inflammation or tumor formation are uniquely susceptible to toxin-mediated injury. The recent observation of ETBF-bearing biofilms in colon biopsies from humans with colon cancer susceptibility loci strongly suggests that ETBF is a driver of colorectal cancer. This article will address ETBF biology from a host-pathobiont perspective, including clinical data, analysis of molecular mechanisms of disease, and the complex ecological context of the human gut.
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Affiliation(s)
- Ezequiel Valguarnera
- Department of Pediatrics, Washington University School of Medicine, 660 S. Euclid Ave. Box 8208, St. Louis, MO 63110
| | - Juliane Bubeck Wardenburg
- Department of Pediatrics, Washington University School of Medicine, 660 S. Euclid Ave. Box 8208, St. Louis, MO 63110.
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8
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Hecht AL, Casterline BW, Choi VM, Bubeck Wardenburg J. A Two-Component System Regulates Bacteroides fragilis Toxin to Maintain Intestinal Homeostasis and Prevent Lethal Disease. Cell Host Microbe 2017; 22:443-448.e5. [PMID: 28943327 PMCID: PMC5839110 DOI: 10.1016/j.chom.2017.08.007] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2017] [Revised: 05/26/2017] [Accepted: 08/15/2017] [Indexed: 01/03/2023]
Abstract
Intestinal microbes are recognized for their role in human disease. Enterotoxigenic Bacteroides fragilis (ETBF) has been implicated in inflammatory bowel disease and colorectal cancer; however, colonization alone is insufficient to cause these illnesses. We hypothesized that homeostasis in healthy carriers is maintained by colonic mucus, the major constituent of which is the glycoprotein Muc2. We found that Muc2-deficient mice succumb to lethal disease from ETBF colonization in a B. fragilis toxin (BFT)-dependent manner. We identify a toxin regulator, the two-component system RprXY, which suppresses BFT expression in vitro and in vivo. Overexpression of either component was sufficient to prevent lethal disease in Muc2-deficient mice. Our studies demonstrate that homeostasis in the context of ETBF colonization is dependent on a dynamic interaction between intestinal mucus, a bacterial toxin, and a toxin regulatory system. Regulation of virulence may offer a therapeutic target to maintain intestinal homeostasis in susceptible patients.
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Affiliation(s)
- Aaron L Hecht
- University of Chicago, Department of Microbiology, Chicago, IL 60637, USA; University of Chicago, Interdisciplinary Scientist Training Program, Chicago, IL 60637, USA
| | - Benjamin W Casterline
- University of Chicago, Department of Microbiology, Chicago, IL 60637, USA; University of Chicago, Interdisciplinary Scientist Training Program, Chicago, IL 60637, USA
| | - Vivian M Choi
- University of Chicago, Department of Microbiology, Chicago, IL 60637, USA; University of Chicago, Interdisciplinary Scientist Training Program, Chicago, IL 60637, USA
| | - Juliane Bubeck Wardenburg
- University of Chicago, Department of Microbiology, Chicago, IL 60637, USA; University of Chicago, Departments of Pediatrics and Microbiology, Chicago, IL 60637, USA.
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9
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Keenan JI, Aitchison A, Purcell RV, Greenlees R, Pearson JF, Frizelle FA. Screening for enterotoxigenic Bacteroides fragilis in stool samples. Anaerobe 2016; 40:50-3. [PMID: 27166180 DOI: 10.1016/j.anaerobe.2016.05.004] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2016] [Revised: 04/21/2016] [Accepted: 05/06/2016] [Indexed: 02/08/2023]
Abstract
Bacteroides fragilis is a commensal bacterium found in the gut of most humans, however enterotoxigenic B. fragilis strains (ETBF) have been associated with diarrhoea and colorectal cancer (CRC). The purpose of this study was to establish a method of screening for the Bacteroides fragilis toxin (bft) gene in stool samples, as a means of determining if carriage of ETBF is detected more often in CRC patients than in age-matched healthy controls. Stool samples from 71 patients recently diagnosed with CRC, and 71 age-matched controls, were screened by standard and quantitative PCR using primers specific for the detection of the bft gene. Bacterial template DNA from stool samples was prepared by two methods: a sweep, where all colonies growing on Bacteroides Bile Esculin agar following stool culture for 48 h at 37 °C in an anaerobic environment were swept into sterile water and heat treated; and a direct DNA extraction from each stool sample. The bft gene was detected more frequently from DNA isolated from bacterial sweeps than from matched direct DNA extractions. qPCR was found to be more sensitive than standard PCR in detecting bft. The cumulative total of positive qPCR assays from both sample types revealed that 19 of the CRC patients had evidence of the toxin gene in their stool sample (27%), compared to seven of the age-matched controls (10%). This difference was significant (P = 0.016). Overall, ETBF carriage was detected more often in CRC patient stool samples compared to controls, but disparate findings from the different DNA preparations and testing methods suggests that poor sensitivity may limit molecular detection of ETBF in stool samples.
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Affiliation(s)
- Jacqueline I Keenan
- Department of Surgery, University of Otago Christchurch, Christchurch, New Zealand.
| | - Alan Aitchison
- Department of Surgery, University of Otago Christchurch, Christchurch, New Zealand
| | - Rachel V Purcell
- Department of Surgery, University of Otago Christchurch, Christchurch, New Zealand
| | - Rosie Greenlees
- Microbiology Department, Canterbury Health Laboratories, Christchurch, New Zealand
| | - John F Pearson
- Biostatistics and Computational Biology Unit, University of Otago Christchurch, Christchurch, New Zealand
| | - Frank A Frizelle
- Department of Surgery, University of Otago Christchurch, Christchurch, New Zealand
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10
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PCR Detection of the Bacteroides fragilis Enterotoxin Gene Relies on Robust Primer Design. J Clin Microbiol 2015; 54:239-40. [PMID: 26491187 DOI: 10.1128/jcm.02785-15] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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11
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Baxter NT, Zackular JP, Chen GY, Schloss PD. Structure of the gut microbiome following colonization with human feces determines colonic tumor burden. MICROBIOME 2014; 2:20. [PMID: 24967088 PMCID: PMC4070349 DOI: 10.1186/2049-2618-2-20] [Citation(s) in RCA: 207] [Impact Index Per Article: 20.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Accepted: 06/04/2014] [Indexed: 05/06/2023]
Abstract
BACKGROUND A 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. RESULTS We 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. CONCLUSION Our 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.
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Affiliation(s)
- Nielson T Baxter
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, USA
| | - Joseph P Zackular
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, USA
| | - Grace Y Chen
- Department of Internal Medicine, Division of Hematology and Oncology, University of Michigan, Ann Arbor, Michigan, USA
| | - Patrick D Schloss
- Department of Microbiology and Immunology, University of Michigan, Ann Arbor, Michigan, USA
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12
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Kharlampieva DD, Manuvera VA, Podgorny OV, Kovalchuk SI, Pobeguts OV, Altukhov IA, Alexeev DG, Lazarev VN, Govorun VM. Purification and characterisation of recombinant Bacteroides fragilis toxin-2. Biochimie 2013; 95:2123-31. [PMID: 23954621 DOI: 10.1016/j.biochi.2013.08.005] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2013] [Accepted: 08/06/2013] [Indexed: 12/21/2022]
Abstract
Fragilysin (BFT) is metalloprotease that is secreted by enterotoxigenic Bacteroides fragilis. Studying the mechanism of BFT interaction with intestinal epithelial cells requires a pure protein sample. In this study, we cloned DNA-fragments coding for the catalytic domain of fragilysin-2 and profragilysin-2 into an E. coli expression vector. Purification methods for the recombinant fragilysin-2 catalytic domain and profragilysin-2 were developed. In addition, we obtained mature active fragilysin-2 from recombinant proprotein by limited tryptic digestion. We tested the biological activity of the recombinant protein samples and revealed that E-cadherin was cleaved when HT-29 cells were treated with mature fragilysin-2 but not with profragilysin-2. Azocoll, azocasein and gelatin were not proteolytically cleaved by mature fragilysin-2. Proteins released in culture medium after HT-29 cells treatment with mature active BFT-2 were identified.
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Affiliation(s)
- D D Kharlampieva
- Research Institute for Physico-Chemical Medicine of the Federal Medical and Biological Agency of Russian Federation, Malaya Pirogovskaya Str. 1a, Moscow 119435, Russia.
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13
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Enterotoxigenic Bacteroides fragilis: a rogue among symbiotes. Clin Microbiol Rev 2009; 22:349-69, Table of Contents. [PMID: 19366918 DOI: 10.1128/cmr.00053-08] [Citation(s) in RCA: 264] [Impact Index Per Article: 17.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Enterotoxigenic Bacteroides fragilis (ETBF) strains are strains of B. fragilis that secrete a 20-kDa heat-labile zinc-dependent metalloprotease toxin termed the B. fragilis toxin (BFT). BFT is the only recognized virulence factor specific for ETBF. ETBF strains are associated with inflammatory diarrheal disease in children older than 1 year of age and in adults; limited data suggest an association of ETBF colonization with inflammatory bowel disease flare-ups and colorectal cancer. ETBF secretes one of three highly related BFT isoforms. The relationship between BFT isoform and disease expression is unknown. Although the mechanism of action of BFT is incompletely understood, available data suggest that BFT binds to a specific intestinal epithelial cell receptor, stimulating intestinal cell signal transduction pathways that result in cell morphology changes, cleavage of E-cadherin, reduced colonic barrier function, and increased epithelial cell proliferation and cytokine expression (such as the proinflammatory chemokine interleukin-8). Together, the data suggest that in some hosts, ETBF acts via secretion of BFT to induce colitis. However, the full spectrum of clinical disease related to ETBF and the impact of chronic ETBF colonization on the host remain to be defined.
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14
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Induction of persistent colitis by a human commensal, enterotoxigenic Bacteroides fragilis, in wild-type C57BL/6 mice. Infect Immun 2009; 77:1708-18. [PMID: 19188353 DOI: 10.1128/iai.00814-08] [Citation(s) in RCA: 209] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Enterotoxigenic Bacteroides fragilis (ETBF) causes diarrhea and is implicated in inflammatory bowel diseases and colorectal cancer. The only known ETBF virulence factor is the Bacteroides fragilis toxin (BFT), which induces E-cadherin cleavage, interleukin-8 secretion, and epithelial cell proliferation. A murine model for ETBF has not been characterized. Specific pathogen-free (SPF) C57BL/6J or germfree 129S6/SvEv mice were orally inoculated with wild-type ETBF (WT-ETBF) strains, a nontoxigenic WT strain of B. fragilis (WT-NTBF), WT-NTBF overexpressing bft (rETBF), or WT-NTBF overexpressing a biologically inactive mutated bft (rNTBF). In SPF and germfree mice, ETBF caused colitis but was lethal only in germfree mice. Colonic histopathology demonstrated mucosal thickening with inflammatory cell infiltration, crypt abscesses, and epithelial cell exfoliation, erosion, and ulceration. SPF mice colonized with rETBF mimicked WT-ETBF, whereas rNTBF caused no histopathology. Intestinal epithelial E-cadherin was rapidly cleaved in vivo in WT-ETBF-colonized mice and in vitro in intestinal tissues cultured with purified BFT. ETBF mice colonized for 16 months exhibited persistent colitis. BFT did not directly induce lymphocyte proliferation, dendritic cell stimulation, or Toll-like receptor activation. In conclusion, WT-ETBF induced acute then persistent colitis in SPF mice and rapidly lethal colitis in WT germfree mice. Our data support the hypothesis that chronic colonization with the human commensal ETBF can induce persistent, subclinical colitis in humans.
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15
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Wu S, Rhee KJ, Zhang M, Franco A, Sears CL. Bacteroides fragilis toxin stimulates intestinal epithelial cell shedding and gamma-secretase-dependent E-cadherin cleavage. J Cell Sci 2007; 120:1944-52. [PMID: 17504810 PMCID: PMC3056613 DOI: 10.1242/jcs.03455] [Citation(s) in RCA: 166] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Enterotoxigenic Bacteroides fragilis - organisms that live in the colon - secrete a metalloprotease toxin, B. fragilis toxin. This toxin binds to a specific intestinal epithelial cell receptor and stimulates cell proliferation, which is dependent, in part, on E-cadherin degradation and beta-catenin-T-cell-factor nuclear signaling. Gamma-secretase (or presenilin-1) is an intramembrane cleaving protease and is a positive regulator of E-cadherin cleavage and a negative regulator of beta-catenin signaling. Here we examine the mechanistic details of toxin-initiated E-cadherin cleavage. B. fragilis toxin stimulated shedding of cell membrane proteins, including the 80 kDa E-cadherin ectodomain. Shedding of this domain required biologically active toxin and was not mediated by MMP-7, ADAM10 or ADAM17. Inhibition of gamma-secretase blocked toxin-induced proteolysis of the 33 kDa intracellular E-cadherin domain causing cell membrane retention of a distinct beta-catenin pool without diminishing toxin-induced cell proliferation. Unexpectedly, gamma-secretase positively regulated basal cell proliferation dependent on the beta-catenin-T-cell-factor complex. We conclude that toxin induces step-wise cleavage of E-cadherin, which is dependent on toxin metalloprotease and gamma-secretase. Our results suggest that differentially regulated beta-catenin pools associate with the E-cadherin-gamma-secretase adherens junction complex; one pool regulated by gamma-secretase is important to intestinal epithelial cell homeostasis.
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Affiliation(s)
- Shaoguang Wu
- Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans St, CRB2 Bldg Suite 1M.05, Baltimore, MD 21231, USA
| | - Ki-Jong Rhee
- Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans St, CRB2 Bldg Suite 1M.05, Baltimore, MD 21231, USA
| | - Ming Zhang
- Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans St, CRB2 Bldg Suite 1M.05, Baltimore, MD 21231, USA
| | - Augusto Franco
- Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans St, CRB2 Bldg Suite 1M.05, Baltimore, MD 21231, USA
| | - Cynthia L. Sears
- Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans St, CRB2 Bldg Suite 1M.05, Baltimore, MD 21231, USA
- Division of Gastroenterology, Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans St, CRB2 Bldg Suite 1M.05, Baltimore, MD 21231, USA
- Author for correspondence ()
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Sears CL, Buckwold SL, Shin JW, Franco AA. The C-terminal region of Bacteroides fragilis toxin is essential to its biological activity. Infect Immun 2006; 74:5595-601. [PMID: 16988234 PMCID: PMC1594940 DOI: 10.1128/iai.00135-06] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
To evaluate the role of the C-terminal region in Bacteroides fragilis toxin (BFT) activity, processing, and secretion, sequential C-terminal truncation and point mutations were created by site-directed mutagenesis. Determination of BFT activity on HT29/C1 cells, cleavage of E-cadherin, and the capacity to induce interleukin-8 secretion by wild-type BFT and C-terminal deletion mutants showed that deletion of only 2 amino acid residues at the C terminus significantly reduced BFT biological activity and deletion of eight or more amino acid residues obliterated BFT biologic activity. Western blot and reverse transcription-PCR analyses indicated that BFT mutants lacking seven or fewer amino acid residues in the C-terminal region are processed and expressed similar to wild-type BFT. However, BFT mutants lacking eight or more amino acids at the C terminus are expressed similar to wild-type BFT but are unstable. We concluded that the C terminus of BFT is not tolerant of modest amino acid deletions, suggesting that it is biologically important for BFT activity.
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Affiliation(s)
- Cynthia L Sears
- Division of Infectious Diseases, Johns Hopkins University School of Medicine, Cancer Research Building II, 1550 Orleans Street, Loading Dock, Room 1M04, Baltimore, MD 21205, USA
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Buckwold SL, Shoemaker NB, Sears CL, Franco AA. Identification and characterization of conjugative transposons CTn86 and CTn9343 in Bacteroides fragilis strains. Appl Environ Microbiol 2006; 73:53-63. [PMID: 17071793 PMCID: PMC1797145 DOI: 10.1128/aem.01669-06] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The related genetic elements flanking the Bacteroides fragilis pathogenicity island (PAI) in enterotoxigenic B. fragilis (ETBF) 86-5443-2-2 and also present in pattern III nontoxigenic B. fragilis (NTBF) NCTC 9343 were defined as putative conjugative transposons (CTns), designated CTn86 and CTn9343, respectively (A. A. Franco, J. Bacteriol. 181:6623-6633, 2004). CTn86 and CTn9343 have the same basic structures except that their encoded transposases have low similarity and CTn9343 lacks the B. fragilis PAI and contains an extra 7-kb region not present in CTn86. In this study, using DNA hybridization and PCR analysis, we characterized the genetic element flanking the PAI in a collection of ETBF strains and the related genetic elements in a collection of NTBF pattern III strains. We found that in all 123 ETBF strains, the PAI is contained in a genetic element similar to CTn86. Of 73 pattern III strains, 26 (36%) present a genetic element similar to CTn9343, 38 (52%) present a genetic element similar to CTn9343 but lack the 7-kb region that is also absent in CTn86 (CTn9343-like element), and 9 (12%) present a genetic element similar to CTn86 but lacking the PAI (CTn86-like element). In addition to containing CTn86, ETBF strains can also contain CTn9343, CTn9343-like, or CTn86-like elements. CTn86, CTn9343, CTn86-like, and CTn9343-like elements were found exclusively in B. fragilis strains and predominantly in division I, cepA-positive strains.
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Affiliation(s)
- Simy L Buckwold
- Division of Infectious Diseases, Johns Hopkins University School of Medicine, Cancer Research Building II, 1550 Orleans Street, Loading Dock, Room 1M04, Baltimore, MD 21205, USA
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Wu S, Shin J, Zhang G, Cohen M, Franco A, Sears CL. The Bacteroides fragilis toxin binds to a specific intestinal epithelial cell receptor. Infect Immun 2006; 74:5382-90. [PMID: 16926433 PMCID: PMC1594844 DOI: 10.1128/iai.00060-06] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
The Bacteroides fragilis toxin (BFT) is the only known virulence factor of enterotoxigenic B. fragilis. BFT has previously been shown to act, at least in part, through cleavage of the intercellular adhesion protein E-cadherin. A specific cellular receptor for BFT has not been identified. The goal of this study was to determine if the initial interaction of BFT with intestinal epithelial cells was consistent with binding to a specific cellular receptor. Purified BFT was labeled with a fluorophore or iodide to assess specific cellular binding and the properties of BFT cellular binding. BFT binds specifically to intestinal epithelial cell lines in vitro in a polarized manner. However, specific binding occurs only at 37 degrees C and requires BFT metalloprotease activity. The BFT receptor is predicted to be a membrane protein other than E-cadherin or a known protease-activated receptor (PAR1 to PAR4). BFT binding is resistant to acid washing, suggesting an irreversible interaction. Sugar or lipid residues do not appear to be involved in the mechanism of BFT cellular binding, but binding is sensitive to membrane cholesterol depletion. We conclude that intestinal epithelial cells in vitro possess a specific membrane BFT receptor that is distinct from E-cadherin. The data favor a model in which the metalloprotease domain of BFT processes its receptor protein, initiating cellular signal transduction that mediates the biological activity of BFT. However, activation of recognized protease-activated receptors does not mimic or block BFT biological activity or binding, suggesting that additional protease-activated receptors on intestinal epithelial cells remain to be identified.
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Affiliation(s)
- Shaoguang Wu
- Division of Infectious Diseases, Department of Medicine, Johns Hopkins University School of Medicine, 1550 Orleans St., Baltimore, MD 21231, USA
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19
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Franco AA, Buckwold SL, Shin JW, Ascon M, Sears CL. Mutation of the zinc-binding metalloprotease motif affects Bacteroides fragilis toxin activity but does not affect propeptide processing. Infect Immun 2005; 73:5273-7. [PMID: 16041055 PMCID: PMC1201259 DOI: 10.1128/iai.73.8.5273-5277.2005] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
To evaluate the role of the zinc-binding metalloprotease in Bacteroides fragilis toxin (BFT) processing and activity, the zinc-binding consensus sequences (H348, E349, H352, G355, H358, and M366) were mutated by site-directed-mutagenesis. Our results indicated that single point mutations in the zinc-binding metalloprotease motif do not affect BFT processing but do reduce or eliminate BFT biologic activity in vitro.
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Affiliation(s)
- Augusto A Franco
- Division of Infectious Diseases, Johns Hopkins University School of Medicine, Ross Bldg., Rm. 1167, 1147B Rutland Ave., Baltimore, MD 21205, USA.
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Franco AA. The Bacteroides fragilis pathogenicity island is contained in a putative novel conjugative transposon. J Bacteriol 2004; 186:6077-92. [PMID: 15342577 PMCID: PMC515173 DOI: 10.1128/jb.186.18.6077-6092.2004] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
The genetic element flanking the Bacteroides fragilis pathogenicity island (BfPAI) in enterotoxigenic B. fragilis (ETBF) strain 86-5443-2-2 and a related genetic element in NCTC 9343 were characterized. The results suggested that these genetic elements are members of a new family of conjugative transposons (CTns) not described previously. These putative CTns, designated CTn86 and CTn9343 for ETBF 86-5443-2-2 and NCTC 9343, respectively, differ from previously described Bacteroides species CTns in a number of ways. These new transposons do not carry tetQ, and the excision from the chromosome to form a circular intermediate is not regulated by tetracycline; they are predicted to differ in their mechanism of transposition; and their sequences have very limited similarity with CTnDOT or other described CTns. CTn9343 is 64,229 bp in length, contains 61 potential open reading frames, and both ends contain IS21 transposases. Colony blot hybridization, PCR, and sequence analysis indicated that CTn86 has the same structure as CTn9343 except that CTn86 lacks a approximately 7-kb region containing truncated integrase (int2) and rteA genes and it contains the BfPAI integrated between the mob region and the bfmC gene. If these putative CTns were to be demonstrated to be transmissible, this would suggest that the bft gene can be transferred from ETBF to nontoxigenic B. fragilis strains by a mechanism similar to that for the spread of antibiotic resistance genes.
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Affiliation(s)
- Augusto A Franco
- Division of Infectious Diseases, Johns Hopkins University School of Medicine, Ross Bldg., Rm. 1167, 720 Rutland Ave., Baltimore, MD 21205, USA.
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Abstract
In this review, we focus on a group of mobile genetic elements designated pathogenicity islands (PAI). These elements play a pivotal role in the virulence of bacterial pathogens of humans and are also essential for virulence in pathogens of animals and plants. Characteristic molecular features of PAI of important human pathogens and their role in pathogenesis are described. The availability of a large number of genome sequences of pathogenic bacteria and their benign relatives currently offers a unique opportunity for the identification of novel pathogen-specific genomic islands. However, this knowledge has to be complemented by improved model systems for the analysis of virulence functions of bacterial pathogens. PAI apparently have been acquired during the speciation of pathogens from their nonpathogenic or environmental ancestors. The acquisition of PAI not only is an ancient evolutionary event that led to the appearance of bacterial pathogens on a timescale of millions of years but also may represent a mechanism that contributes to the appearance of new pathogens within a human life span. The acquisition of knowledge about PAI, their structure, their mobility, and the pathogenicity factors they encode not only is helpful in gaining a better understanding of bacterial evolution and interactions of pathogens with eukaryotic host cells but also may have important practical implications such as providing delivery systems for vaccination, tools for cell biology, and tools for the development of new strategies for therapy of bacterial infections.
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Affiliation(s)
- Herbert Schmidt
- Institut für Medizinische Mikrobiologie und Hygiene, Medizinische Fakultät Carl Gustav Carus, Technische Universität Dresden, Dresden, Germany.
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Abstract
Bacteroides fragilis are both key commensals and important human pathogens. Particular strains of B. fragilis, termed enterotoxigenic B. fragilis (ETBF), are recently identified enteric pathogens of children and adults. These strains are distinguished by secretion of a 20kDa metalloprotease toxin (B. fragilis toxin or BFT), the first recognized and only established toxin to date for B. fragilis. Three isotypes of BFT are encoded by distinct bft loci contained within a 6kb chromosomal region unique to ETBF strains termed the B. fragilis pathogenicity island (BfPAI). Experimental studies have suggested that the cellular target for BFT is E-cadherin, the primary protein of the zonula adherens. It is postulated that BFT cleavage of E-cadherin is critical in precipitating the intracellular events culminating in the two established activities for BFT; namely, stimulation of secretion in ligated intestinal segments in several animal species and alteration of cellular morphology only in epithelial cells that retain the ability to polarize and form a tight junctional complex. Future studies will be directed to characterizing in greater detail both the molecular genetics of the BFT toxin and the precise steps in its cellular mechanism of action.
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Affiliation(s)
- C L Sears
- Johns Hopkins University School of Medicine, Division of Infectious Diseases, Department of Medicine, Baltimore, MD 21205-2196, USA.
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