Lecture_21_Digestive_System_ch22_Part2.pdf
Transcript
CHAPTER 22 Infections of the Digestive System – Part 2 Copyright © 2021 W. W. Norton & Company Rotavirus Rotavirus Characteristics § Rotaviruses are non-enveloped double-stranded RNA (dsRNA) viruses § complex architecture: three concentric capsids that surround a genome of 11 segments of dsRNA. §...
CHAPTER 22 Infections of the Digestive System – Part 2 Copyright © 2021 W. W. Norton & Company Rotavirus Rotavirus Characteristics § Rotaviruses are non-enveloped double-stranded RNA (dsRNA) viruses § complex architecture: three concentric capsids that surround a genome of 11 segments of dsRNA. § Genes encode: • Structural proteins à host specificity, cell entry, viral transcription, epitopes for immune responses • non-structural proteins: involved in genome replication & interfering with innate immunity (e.g. NSP1 and viral enterotoxin NSP4) “rota” comes from wheel-like appearance The RNA segments encode: • six structural viral proteins (VP1 – 4, 6, 7,) • six non-structural proteins (NSP1 – 6) Rotavirus Relevance of Rotaviruses • Widespread Infection: Rotaviruses infect nearly every child globally by age 3–5. • Global Impact: In 2013, they caused 200,000+ child fatalities, with consistent prevalence (30– 50%) in hospitalized cases. • Low-Income Challenges: Over 90% of fatal cases are in lowincome countries due to limited healthcare, insufficient hydration, and comorbid conditions. Rotavirus VP4 :lipid raft interactions Triggered by low Ca2+ levels DLP = double layered particle VP1,3, bind newly transcribed RNA Rotavirus infectious Cycle • Rotaviruses attach to glycan receptors via VP4, concentrated at lipid rafts, initiating viral entry. • Internalization leads to low endosomal calcium, triggering the release of transcriptionally Triple-layered particle active DLP into the cytoplasm. • Viroplasms aid in packaging, and the triple-layered particle non-structural protein 4 assembly involves DLP binding to (NSP4; an intracellular receptor) NSP4, ER budding, and the acquisition of outer capsid VP2 & 6 create structural proteins VP4 and VP7. layers around new DLP (future capsid) Rotavirus Histopathological images of the duodenum of a mouse pup infected with a murine rotavirus strain (EDIM), 48 hours after infection. Vacuolization of enterocytes VP6 staining in Infected mouse enterocytes Pathology of Rotavirus Infection • Rotavirus predominantly infects mature enterocytes at the middle and top of intestinal villi – indicated by immunofluorescent labelling of rotavirus antigen viral protein 6. • Vacuolization of enterocytes in the top and middle of intestinal villi can be observed with rotavirus infection; crypt cells are unaffected. Rotavirus Mechanism of Rotavirus-induced Diarrhea • Initiation: Rotavirus non-structural protein 4 (NSP4) is released, stimulating enterochromaffin cells (EC) to release 5hydroxytryptamine (5-HT). • Effect of 5-HT: 5-HT, a neurotransmitter, activates 5-HT3 receptors on intrinsic primary afferent nerves, increasing gastrointestinal motility and inducing nausea/vomiting. • Enteric Nervous System Activation: This activation leads to increased intestinal motility and stimulation of nerves in the submucosal plexus, causing the release of vasoactive intestinal peptide (VIP) from nerve endings adjacent to crypt Rotavirus Mechanism of Rotavirus-induced Diarrhea (con’td) • VIP Signaling: VIP signaling raises cellular cAMP levels, resulting in the secretion of sodium chloride (NaCl) and water into the intestinal lumen, ultimately causing diarrhea. • Vomiting Reflex: Rotavirus can activate the vomiting center in the brainstem. The virus or NSP4 stimulates vagal afferents to the vomiting center by releasing 5-HT from ECs in the gut, triggering the vomiting reflex. • Clinical Intervention: 5-HT3 receptor antagonists are employed to attenuate vomiting in children with acute gastroenteritis, disrupting the vomiting reflex induced by the rotavirus infection. Rotavirus Immune Evasion Strategies • In human cells in vitro, evasion of the innate IFN response is mediated by rotavirus non-structural protein 1 (NSP1) through inhibition of NF-κB activation • via degradation of F-box/WD repeat-containing protein 1A (BTRC; also known as β-TrCP) • NSP1 can also block type I and type III IFN responses by inhibiting STAT1 activation • Other viral proteins (VPs) might be involved in the suppression of the IFN response through inactivation of MAVS. IFNAR1, IFN-α/β receptor 1; IκB, inhibitor of nuclear factor-κB; IKK-ε, inhibitor of NF-κB kinase subunit ε; JAK1, Janus kinase 1; ISRE, IFN-stimulated response element; TBK1, TANK-binding kinase 1; TYK2, non-receptor tyrosine kinase TYK2. Rotavirus Relevance of Rotaviruses • Transmission: Mainly fecal-oral route • Diagnosis: PCR assays (for rotavirus alone or in multipathogen panels) or serologic assays • Treatment: Supportive – disease is self-limited, lasting only a few days. – oral rehydration therapy to prevent dehydration. • Prevention: Vaccination • During first year of an infant’s life, rotavirus vaccines provide up to 87% protection against rotavirus illness Stool PCR test Oral delivery of vaccine two available vaccines: RotaTeq® licensed in 2006; given in 3 doses @ ages 2, 4 & 6 months Rotarix® licensed in 2008; given in two doses @ ages 2 & 4 months Hepatitis § The A, B, Cs of hepatitis. All are RNA viruses except for B Hepatitis Strain Transmission Characteristics A Fecal-oral, food borne Self-limiting, no asymptomatic carriers or liver disease. B Exchange of blood or body fluids (sexual contact) Often no symptoms are displayed, carriers of virus are common, and liver damage is seen in 30% of cases. C Exchange of blood or body fluids (sexual contact) Mild initial disease, 70% progress to chronic infection. Risk of liver failure and cancer. D E Only causes disease if coinfection occurs with hepatitis B virus. Fecal-oral route, typically waterborne Both acute and chronic disease are possible. Very difficult to detect with current tests. Uncommon in the United States. 10 22.5 Bacterial Infections of the Gastrointestinal Tract Section Objectives § Categorize GI infections by bacterial pathogenic mechanisms. § Correlate bacterial virulence mechanisms to GI disease symptoms. § Relate the treatment of GI infections to virulence of GI pathogens. § Evaluate treatment and prevention methods used for bacterial infections of the GI tract. 11 Peptic Ulcers § Helicobacter pylori • Gram-negative spirochete • Phylum Proteobacteria (Class Epsilonproteobacteria) • ubiquitous and infects ~ half of the human population worldwide § Identified in 1983 by Barry Marshall and Robin Warren as causative agent of peptic ulcer disease (Nobel Prize 2005) § Since this discovery involved in stomach ulceration & gastric cancer § Symptoms – Dyspepsia, upper abdominal pain, bloating, belching, nausea 12 GASTRIC INFECTIONS Damage § H. pylori colonizes the human gastric mucosa and causes superficial gastritis within weeks. § Over years, H. pylori–induced gastritis can either remain clinically asymptomatic or lead to different disease outcomes: § duodenal ulcer via hyperacidity § gastric adenocarcinoma via chronic inflammation § MALT or non-Hodgkin lymphoma (rare) Normal Gastric Mucosa Active Gastritis 13 GASTRIC INFECTIONS Encounter and adherence 1. Initial steps of H. pylori colonization include acid adaptation, motility, and chemotaxis to the mucus layer and gastric epithelium. • urease production to neutralize stomach acid • flagella to provide motility à penetrate the mucous layer of the stomach lining. 2. H pylori also colonizes the gastric epithelium via adhesin-mediated adherence to epithelial cell receptors. • initial binding via Blood-group antigen binding adhesin (BabA) • Chronic infection via Sialic acid-binding adhesin (SabA) H pylori virulence factors associated with adherence, persistence, and damage. 14 GASTRIC INFECTIONS Encounter and adherence 3. H pylori initiates epithelial damage via release & delivery of effector proteins that induce an array of pathologic effects on the gastric epithelium. § cytotoxin-associated gene (cagA) § Secreted into cell via T4SS § Impairs epithelial barrier integrity by disrupting Tight junctions and Adherens Junctions à antigen leakage § Tyrosine Phosphorylated in vivo à increased epithelial proliferation and motility (linked to gastric cancer). § Present in 70% of H pylori infections and 90% of cases of peptic ulcer disease § Vacuolating cytotoxin A (VacA) § Present in most strains of H. pylori § Leads to vacuolation § Forms transmembrane pores deregulating selective permeability of membrane § Causes apoptosis Formation of vacuoles or vacuole-like structures within cells 15 If you are curious (Bonus Question on Test) Both CagA and T4SS encoded with the Cag Pathogenicity Island (PAI). 16 Gastric INFECTIONS (ELISA – Enzyme-linked Immunosorbent Assay) Invasive § Urease test of biopsies: tests ammonia production via pH indicator. § Culture can be problematic due to fastidious nature of H. pylori growth § Histology allows visualization of pathogen in-situ using histologic stains Non-Invasive § Urea breath tests: Following ingestion of carbon-labeled urea, H. pylori+ persons will produce ammonia and labeled CO2, the latter detected by breath test § Good method to test eradication § Serology: measure levels of circulating H.pylori-specific IgG antibodies via(ELISA) § sensitive and specific for primary diagnosis of H pylori infection, but limited for post-treatment assessment due to maintenance of serologic titires. § Stool antigenic tests: ELISA of fecal material § Accurate in determining post-treatment H. pylori responses. 17 Case History: Field Trip Diarrhea ‒ 1 § Tammy, a 6-year-old girl from Montgomery County, Pennsylvania, arrived at a hospital’s emergency department with bloody diarrhea, a temperature of 39°C (102.2°F), abdominal cramping, and vomiting. § Admitted to the hospital 5 days after a field trip to the local dairy farm. The child’s health history was otherwise unremarkable. § parents were asked about Tammy’s activities during the trip. The parents confirmed that Tammy bought a snack while at the farm. 18 Case History: Field Trip Diarrhea ‒ 2 § The lab reported that her fecal smear was positive for leukocytes and contained Gram-negative rods that produced Shiga toxins 1 and 2. § Further testing of the isolate’s serotype revealed E. coli O157:H7. § By this time, Tammy had developed additional problems. • Her face and hands had become puffy, • decreased urine output despite being given IV fluids (suggesting kidney damage), • beginning to develop some neurological abnormalities. • thrombocytopenia (reduced blood platelet count) • confirmed hemolytic uremic syndrome (HUS, renal failure). § Tammy was treated with intravenous fluid and electrolyte replacement. Antibiotics were not administered, and she eventually recovered. 19 Intestinal Diseases Caused by Gram-Negative Bacteria – 1 § Escherichia coli gastroenteritis • Enterotoxigenic E. coli (ETEC) – Produces labile toxin – Causes secretory, watery diarrhea – No animal reservoirs • Enteroinvasive E. coli (EIEC) – Causes bloody diarrhea similar to that caused by Shigella • Enterohemorrhagic E. coli (EHEC) – Shiga toxin – Causes bloody diarrhea – In severe cases EHEC can lead to hemolytic uremia syndrome and thrombocytopenic purpura. 20 Intestinal Diseases Caused by Gram-Negative Bacteria – 2 § Shigellosis • Bloody diarrhea • Also called bacillary dysentery • Similar pathogenesis to EIEC • No animal reservoir, but is transmitted between humans through fecal-oral route via food or water • Symptoms include – – – – Abdominal cramping Fever Vomiting Watery diarrhea 21 Salmonella diversity § Salmonella genus has two species, each with many subspecies and/or serovars (Table 14.2). • S. enterica (Type species) – 6 subspecies, ~2557 serovars • S. bongori, – 22 serovars • Subspecies are differentiated genomically and/or biochemically § S. enterica subsp. enterica serovars frequently linked to foodborne illness include: • Enteritidis • Typhimurium • Newport § . CHARACTERISTICS OF DISEASE: Symptoms and Treatment ● . Human Salmonella infections can lead to several clinical conditions, including ▶ enteric (typhoid) fever ▶ enterocolitis ▶ systemic infections PATHOGENICITY AND VIRULENCE FACTORS: Attachment and Invasion § Salmonellae must successfully compete with gut microbiota for suitable attachment sites on the intestinal wall. § Key virulence factors dictating invasive infection are encoded within two major Salmonella Pathogenicity Islands: SPI-1 and SPI-2 • During Infection of IEC, SPI-1-encoded Type III secretion system (T3SS) injects effector proteins into epithelial cells, à cytoskeletal rearrangements and membrane ruffling. • Bacteria enter host cell cytosol via endocytosis and activate the SPI-2encoded T3SS system inside the Salmonella-containing vacuole. § Whether serotype is Typhoidal or NonTyphoidal dictates how Salmonella uses Büttner Microbiol. Mol. Biol. Rev. 2012; these virulence factors for pathogenesis Daniela doi:10.1128/MMBR.05017-11 First: translocon; second, effectors Intestinal Diseases Caused by Gram-Negative Bacteria – 4 § Salmonellosis • Two major diseases are typhoid fever and enterocolitis. • Typhoid fever – No animal reservoir – Associated with food preparation – Intermittent fevers and diarrhea for 1‒3 weeks • Enterocolitis – Associated with animal contact – Short-term illness lasts 6‒48 hours 25 PATHOGENICITY AND VIRULENCE FACTORS: Attachment and Invasion Additional virulence determinants § capsular polysaccharide Vi antigen • Mask antigen § Flagellin • Motility and antigenicity § LPS • O-antigen lengths § Siderophores • Sequestering iron § Enterotoxins • Induce diarrhea § Porins • Outer membrane • Regulate nutrient and antibiotic influx Typhoidal Non-Typhoidal Intestinal Diseases Caused by Gram-Negative Bacteria – 7 § Campylobacter enterocolitis overview • Gram-negative, corkscrew shape • Number one cause of diarrhea worldwide • Transmitted through consumption of poorly handled or undercooked meat and unpasteurized milk • Immunocompromised patients can experience disseminated disease. – Pancreas, gallbladder, heart muscles, or peritoneum • Rarely, infection causes an autoimmune disease called Guillain-Barré syndrome. 27 Campylobacter spp. Campylobacter spp. • Phylum Proteobacter • Family Campylobacteraceae. – Also includes Arcobacter spp. § Gram-negative, non-spore-forming rods • curved, S-shaped, or spiral § 0.2 -0.9 µm wide; 0.5 - 5 µm long. § motile via single polar unsheathed flagellum at one or both ends. § most species microaerophilic (5% oxygen and 10% carbon dioxide), § metabolism via respiration § genomes ~1/3 size of E. coli https://s3-eu-central1.amazonaws.com/onlinehygienefoodsafety/wpcontent/uploads/hygienefoodsafety/2019/01/23074116/AR S_Campylobacter_jejuni-2.jpg Relevance of Campylobacter Global § 1978 - 2014: >57,000 Campylobacteriosis cases were associated with 504 outbreaks globally National § Campylobacter infections are the 3rd leading cause of food-borne illnesses and hospitalizations. § Illnesses/yr: 145,000 Silva et al, 2011 § Hospitalizations/yr: 565 § Deaths/yr: 5 Campylobacter infection: CHARACTERISTICS OF DISEASE Most Campylobacter spp. associated with intestinal infection. C. jejuni and C. coli most frequently associated with diarrheal disease: • difficult to distinguish; ~ 5 - 10% of cases attributed to C. jejuni actually due to C. coli; Causes a spectrum of illness à asymptomatic to severely ill. Symptoms: fever, abdominal cramping, diarrhea (with or without blood) that lasts several days to >1 week. infections usually self-limiting • relapses occur in ~ 10% of untreated patients recurrence of abdominal pain is common deaths directly attributable to C. jejuni infection rarely reported C. jejuni infected Pig intestine Campylobacter: RESERVOIRS AND OUTBREAKS Routes of human infection from resevoirs § colonizes the chicken GI tract (primarily the mucus layer) in high numbers • passed between chicks within a flock via faecal–oral route. § C. jejuni can enter the water supply, • Can associate with protozoans (e.g. amoebae). • Farm water à ingestion by livestock § infects humans directly through drinking water or via consumption of contaminated animal products, • E.g. unpasteurized milk or meat, particularly poultry. § In humans, C. jejuni can invade the gut epithelial layer à resulting in inflammation and diarrhoea Young et al, Nat Rev Micro, 2007 VIRULENCE FACTORS AND MECHANISMS OF PATHOGENICITY Cell Association and Invasion § uptake of C. jejuni by host cells occurs by its intimate binding with the host cell surface using many types of adhesins. § Upon contact, C. jejuni produces at least 14 new proteins. • corresponds to a rapid increase in uptake and changes in the host cell membrane. § § § At a later point, other proteins are made and secreted into the cytoplasm of host target cells. Attachment and internalization • Unclear mechanisms of internalization – zipper vs. trigger • Following attachment and internalization, cells release chemokines that promote the recruitment of white blood cells to the site of the infection. C. jejuni-induced cell death may enhance pathogen survival and spread Silva et al, 2012 Campylobacter spp: VIRULENCE FACTORS AND MECHANISMS OF PATHOGENICITY Mucus-Campylobacter interactions: humans vs. chickens Humans § C. jejuni circumvents the mucus layer in humans and interacts with the intestinal epithelial cells to stimulate chemokine (IL-8) production. • IL-8 causes the recruitment of dendritic cells (DC), macrophages and neutrophils, which interact with C. jejuni § à massive pro-inflammatory response and increases in the corresponding cytokines. Chickens § C. jejuni resides in mucus layer in chicken intestines; non invasive. § Can induce cytokine production (IL-1β, IL-6) and intracellular NO synthase from epithelial cells but no overt inflammation § Host response directed to tolerance vs. inflammation Young et al, Nat Rev Micro, 2007 Campylobacter spp: VIRULENCE FACTORS AND MECHANISMS OF PATHOGENICITY Toxins § The cytolethal distending toxin (CDT) holotoxin consists of three subunits, CdtA, CdtB and CdtC. § CdtA and CdtC are thought to bind to an unknown receptor on the host cell surface. § CDT is taken up into host cells by way of clathrin-coated pits. § CdtB nuclear localization signals likely promote its active transport into nucleus § Promotes double-strand DNA breaks and cell-cycle arrest à cell death and increased permeability § Also impairs adaptive immune responses leading to persistent infection § Damage is excacerbated by toxin induced macrophage dependent inflammation Campylobacter spp: VIRULENCE FACTORS AND MECHANISMS OF PATHOGENICITY Toxins § The cytolethal distending toxin (CDT) holotoxin consists of three subunits, CdtA, CdtB and CdtC. § CdtA and CdtC are thought to bind to an unknown receptor on the host cell surface. § CDT is taken up into host cells by way of clathrin-coated pits. § CdtB nuclear localization signals likely promote its active transport into nucleus § Promotes double-strand DNA breaks and cell-cycle arrest à cell death and increased permeability § Also impairs adaptive immune responses leading to persistent infection § Damage is excacerbated by toxin induced macrophage dependent inflammation Campylobacter spp: VIRULENCE FACTORS AND MECHANISMS OF PATHOGENICITY Autoimmune Diseases § Campylobacter infection is a major trigger of Guillian-Barré syndrome (GBS), an auto-immue disease affecting the peripheral nervous system. • Immune-mediated destruction of myelin sheath • Leads to numbness and paralysis of associated tissue § The pathogenesis of GBS induced by is not entirely clear. C. jejuni § Mechanism: molecular mimicry • bacterial lipooligosaccharide (LOS) causes an immune response. • The antibodies produced recognize not only the LPS but also peripheral nerve tissue. Intestinal Diseases Caused by Gram-Negative Bacteria – 8 § Cholera • Vibrio cholerae • Gram-negative curved rod with a single flagellum • Transmitted via fecal-oral route – Contaminated water • “Rice water stools” • Noninvasive; therefore, does not cause fever or bloody stools • Cholera toxin – Promotes Secretory diarrhea – Derived from phage – Key players GM1 (glycolipid), CtxAB, Adenylate Cylase, cAMP, CFTR 37 Intestinal Diseases Caused by Gram-Positive Bacteria – 1 § Much less common than Gram-negative § Most relate to toxins they produce § Four most common types • Listeria monocytogenes • Clostridium difficile • Clostridium perfingens • Staphylococcus aureus 38 Clostridium difficile Clostridium difficile § Phylum Firmicutes, Class Peptostreptococciae § Gram+ spore-forming, rods • Grows in short chains § Obligate anaerobes § most frequent cause of infectious diarrhea in hospitals and long-term care facilities in Canada, as well as in other industrialized countries. vegetative spores Clostridium difficile Disease § C. difficile causes pseudomembranous colitis § Dysbiosis can promote C. difficile outgrowth and infection § Upon infection, C. difficile produces cytolethal toxins § Toxin induced damage and host responses contribute to severe inflammation including extensive inflammatory exudates that lead to fibrin-rich pseudomembrane. pseudomembrane Clostridium difficile Stages of Clostridium difficile life cycle in the human gastrointestinal tract § Three sources of infection: health care, animal and environment. § passage through the stomach eliminates most vegetative cells (but spores survive) § § § § spores germinate and grow out in the duodenum. In cecum and colon: • C. difficile produces toxins (mainly in colon) • Sporulation begins again • Vegetative cells and spores are excreted by the patient during infection. transmission occurs primarily via spores • As C. difficile is an obligate anaerobic bacterium, spores will protect it from O2 rich environment Many host factors influence the Clostridium difficile life cycle & relative numbers of spores and vegetative (metabolically active) cells in the gut. Clostridium difficile Structure and function of the large clostridial toxins § toxin A (TcdA) and TcdB have four functional domains: • glucosyltransferase domain (GTD; red), • autoprotease domain (APD; blue), • the delivery domain (yellow) • and the combined repetitive oligopeptides (CROPS) domain (green) – § 1. 2. 3. 4. 5. 6. 7. Overlay of an electron microscopy reconstruction of the structure of TcdA with the X-ray crystal structure of. binds carbohydrates on the host cell surface to facilitate bacterial entry. The discrete structural and functional domains of the toxins contribute to a multi-step mechanism of intoxication. Toxins bind to one or more receptors (carbohydrate and/or protein) on the cell surface in part via CROPS domain internalized by receptor-mediated endocytosis As the endosome matures, the vacuolar ATPase (V-ATPase) contributes to a decrease in pH acidic pH à conformational change in the toxin delivery domain à pore formation APD and GTD move through pore into the cytosol Inositol hexakisphosphate (InsP6) binds and activates the APD, resulting in the release of the GTD GTD inactivates RHO family proteins àapoptosis and cytopathic ‘rounding’ effects. Decreased pH via endosomal V-ATPase RHO glucosylation Clostridium difficile Structure and function of the large clostridial toxins Glucosyltranserase-independent necrosisinducing Pathway 1. At high concentrations (>0.1 nM) TcdB can promote RAC1 activation 2. NOX complex formation on the endosomal membrane § 3. The fully assembled NOX complex generates superoxide by transferring an electron from NADPH to molecular oxygen 4. Superoxide generation leads to overproduction of reactive oxygen species (ROS) 5. Heightened ROS à necrosis by causing • mitochondrial damage, • lipid peroxidation • protein oxidation NOX complex: • RAS- related C3 botulinum toxin substrate 1 (RAC1) • NADPH oxidase 1 (NOX1), • NADPH oxidase activator 1 (NOXA1), • NADPH oxidase organizer 1 (NOXO1) Clostridium difficile Mechanism of action of Clostridium difficile transferase (CDT) (binary toxin) § CDT is a binary toxin consisting of • CDTa ADP-ribosyltransferase (red) • CDTb protein (yellow and green). § CDTb monomers bind to lipolysis-stimulated lipoprotein receptor (LSR) § CDTb undergoes proteolytic activation and oligomerizes à heptameric prepore § CDTa to the prepore–receptor complex. § This complex enters cells by endocytosis § As endosome matures, the V-ATPase contributes to a decrease in pH. § low endosomal pH triggers pore formation and the translocation of CDTa into cytosol. § Once in the cytosol CDTa, ribosylates actin at arginineà inhibition of G-actin polymerization and increased F-actin depolymerization § The impact on actin causes complete destruction of the actin cytoskeleton & cell death Heptameric prepore Proteolytic activation Decreased pH via endosomal V-ATPase Prepore Receptor complex Pore formation Cdta translocation ribosylation lipolysis-stimulated lipoprotein receptor (LSR), Clostridium difficile Innate immune response of host cells to Clostridium difficile § Clostridium difficile elicits the innate immune response via at least four different effectors: § The large clostridial toxins toxin A (TcdA) and TcdB • act via NLRP3 inflammasome-dependent and independent pathways. § § § Flagellin • Acts through TLR5 Surface layer protein A (SlpA) • acts via myeloid differentiation primary response 88 (MYD88)-dependent pathways through Toll-like receptor 4 (TLR4) Cell wall peptidoglycan fragments • Acts through nucleotide-binding oligomerization domain-containing protein 1 (NOD1)dependent pathway Dashed lines indicate indirect effects. IL-1R1: IL-1 receptor type 1. NLRP3: NOD-, LRR- and pyrin domain-containing 3) Clostridium difficile Don’t memorize this table, just understand it and focus on text Diagnosis and treatment options for C. difficile infections • If Clostridium difficile infection (CDI) is suspected, recommended option is to detect toxins of C. difficile in the stool. • Metronidazole is choice of antibiotic • given orally; in severe cases intravenously. • recurrence after clinical cure (resolution of symptoms) can be observed. • Fidaxomicin (RNA polymerase inhibitor) is a treatment option if the risk of recurrence id high • Faecal microbiota transplant is an effective but non-standard form of treatment (shown by a dashed line). Clostridium difficile Faecal microbiota transplant In faecal microbiota transplant (FMT), faecal material from a healthy donor is collected and processed (blending, filtration) into pills or a solution. • Screened for presence of pathogenic and multidrug-resistant organisms • pill formulations: administered orally • solution formulations: administration by nasoduodenal infusion, colonoscopic infusion or rectal enema Antibiotic treatment generally precedes the administration of the FMT to reduce Clostridium difficile levels. CDI = C. difficile infection Clostridium difficile CDI = C. difficile infection Faecal microbiota transplant (cont’d) Alongside FMT, efforts are ongoing to standardize bacteriotherapy. • signatures of resistance to colonization by C. difficile are identified by microbiomics and metabolomics • Beneficial species cultured and made into defined mixtures for therapy (after validation) Coloured bars indicate diversity of the microbiota, • Alpha diversity is markedly reduced in CDI patient vs. healthy subject.
