Gastrointestinal Infections

Gastrointestinal Infections

1. E. coli

   • EHEC
     • 0157:H7, Gram -ve rod, facultative anaerobe
     • Bacteriophage-derived Shiga toxins (Stx1/Stx2)
       • AB5
       • Bind to glycolipid Gb3 (globotriacylceramide), many in renal epithelium
       • RNA N-glycosidase, ie cleaves nucleobases from ribosomal RNA & inhibits protein synthesis
       • Haemolysin causes Haemolytic Uraemic Syndrome (HUS), Renal failure
     • Incubation: 2-6 days, Infection: 1 week
     • Identification: MALDITOF, serology, selective culture medium, Lactose/Sorbitol fermentor
     • Burgers!!
     • Type III secretion system- see EPEC
   • ETEC
     • Heat-labile or Stable Toxin
       • AB5, acitvates adenyl cyclase, cAMP, activates CFTR, K+/Na+/Cl- ions enter cell, water flows out, diarrhoea!
     • CFA1 fimbriae
   • Type I pilus
     • Regulated expression, ie Phase Variation
       • Environmental signal, fimS (invertible, cis, promoter), fimB (off switch), fimE (on switch), express fimA (pilus rod)/fimC (chaperone)/fimD (OM usher)
         • New findings: HibF another fimS inverter, on switch
         • Signals: pH, temp, osmolarity, nutrient availability
     • Highly immunogenic
     • Motility
   • (a)EPEC
     • "Attaching & Effacing", localised (EPEC) vs diffuse (aEPEC)
     • Pedestal Formation
       • Encoded on LEE (Locus of Enterocyte Effacement)
         • Pathogenicity Island
         • EHEC, EPEC, aEPEC
         • Type III Secretion System injects effector proteins
           • E.g. Injects Tir into membrane, Centre binds intimin, N+C cytoplasmic, phosphorylated by kinases, WASP cascade, actin polymerisation
           • E.g. EspB (homologous to YopD), binds alpha1 antitrypsin, alpha catenin (disrupting adherence junctions), myosin-1c (inhibiting phagocytosis)
           • Functional redundancy, e.g. EspH+EspJ antagonise (opsono-) phagocytosis
           • E.g. NleH, anti-apoptotic factor
         • Acquired via HGT, located on tRNA
         • Subverts cell processes to colonise/multiply
     • EAF plasmid (EPEC Adherence Factor), encodes bundle-forming pilus (not in aEPEC)
   • Case Study: Germany Outbreak 2011
     • E.coli 0104:H4
     • EHEC with virulence genes from EAEC
     • Diagnostics unsuitable, bias for 0157 (no 0157 agglutination, ferments sorbital)
     • Suggested diagnostics: Selective agar (Cefuxime tellurite sorbitol MacConkey agar) --> pink colonies, PCR (intimin target)
     • Future diagnostics: multiplex PCR, microarray

2. Campylobacter

   • C. jejuni
     • Gram -ve, curved/spiral/s-shaped
     • Motile (1-2 flagella)
     • Oxidase +ve
     • Non-fermentor
     • Incubation: 2-10 days, infection: 1 week
     • Autoimmune response possible- similar motif to host proteins--> reactive arthritis or Guillan-Barre Syndrome (myelin, demyelination, paralysis, 019)
     • Zipper vs Trigger model of cell entry. CapF, CiaB, Type III secretion system?
   • C. upsaliensis
   • C. coli
   • C. lari
   • C. fetus
   • C. rectus
   • Mostly poultry
   • Pathogenesis
     • No suitable non-primate models
     • Capsular Polysaccharide: GI/Cell Invasion
     • LOS: adhesion, protection from complement
     • Potential Vaccine
       • Against Serotype HS15
       • Multivalent, CPS
       • CPS-CRM conjugate
       • Ab response in mice but no challenge experiments
     • LuxS Operon
     • Newly Found Virulence Factors

3. Salmonella

   • Enteritis
     • S. enterica serovar typhimurium
     • S. enterica serovar enteritidis
     • G-ve, bacillus, facultative anaerobe
     • Non-fermentor, oxidase -ve
   • Pathogenicity
     • Pathogenicity Islands
       • spv locus, pSLT plasmid
       • SPI1, inv genes
         • Type III Secretion System
           • Injects Effector Proteins for Membrane Ruffling
             • SptP (tyrosine phosphatase, mimics signal transduction)
             • SipA (binds actin, prevents depolymerisation)
             • SopE (activates Rac/Cdc42 for actin polymerisation)
     • 103-106 infectious dose (high)
     • M cells in lamia propia engulfs bacterium, to present to B+T cells BUT survives/multiplies & stimulates inflammatory response (incl. cAMP)
     • Fimbriae
       • Type 1 and/or 3 (fim genes)
       • Plasmid encoded (pef genes)
       • Long polar (lpf genes)
       • Thin aggregative (agf genes)
     • OMP Porins
     • Complement evasion
       • Rck, adhesion factor, inhibits MAC
       • Pgte, protease, cleaves C3, C4 & C5

4. Shigella

   • S. flexneri
   • S. sonnei
   • S. dysenteriae
   • S. boydii
   • Usually water contamination
   • Pathogenesis
     • OspF (MAPK phosphothreonine lyase), inactivates MAPK--> dampens inflammatory response
     • Targets Ubiquitin
       • OspI, deaminates Ubc13 (ubiquitin conjugating enzyme 13)--> dampens NF-KB response
       • IpaH (ubiquitin ligase)
       • Ubiquitin Function: label proteins for destruction or other cell functions, e.g INFLAMMATORY RESPONSE
   • Peak (outbreak?) in 1992
   • Low infectious dose, only 10 bacteria can cause infection!
   • Incubation: 16-72hrs, infection: 2 weeks
   • Haemolysin

5. Rotavirus

   • dsRNA virus
   • 7 serotypes: A-G, A most common
   • No effective antiviral therapy, new targets researched
     • Lipogenesis inhibitors reduce viral replication, e.g. triacsin C (fungi) analogues inhibit ACSL, analogue E=amino-benzinoic acid ED50=0.1um
       • IN VITRO!!
   • Damages vili
   • Malabsorption of fluid
   • Infection 6hrs-3days
   • NSP4, enterotoxic effects
   • New vaccine introduced in UK: Rotarix (GSK), attenuated live oral vaccine, for 6+wks then 4wks later, since v common in <5yr olds
   • Vomiting & diarrhoea

6. Norovirus

   • RNA virus
   • Infection: 24-48hrs
   • Vomiting & diarrhoea
   • No animal model & difficult to culture
   • Five genogroups: GI-GV, GI &GII most common
   • Highly contagious