Cameron Feb 20-23 – Flashcards
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| Microbial Content within the Host |
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| -About a 1:1 ratio of 30 trillion human cells to 30 trillion bacteria cells -Colon and teeth have richest proportion of bacterial cells 5000-10000 different bacterial species -Most variety found in skin and intestines |
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| The Three main surfaces (substrata) of Microbial Attachment to the Host |
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| • skin • mucosae • teeth Bacteria must be flexible in attachment due to range of surfaces --> Streptococci and staphylococci attach to a lot of different body parts |
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| The Three Steps of Colonization of Host Cell Surfaces |
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| 1. Non-specific interactions (first, weak entrance) ? Hydrophobic interactions ? Cation-bridging 2. Initial anchoring adhesion (weak, smapling surface) – Pili, S-layer, capsule, flagella 3. Tight adhesion (receptor-ligand interaction) – Specific adhesins |
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| Non-Specific Interations |
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| • Hydrophobic interactions: – non-polar molecules on bacterial surface/host • Cation-bridging: – Divalent metal ions (eg. Ca2+) - Bridges with + ions as the cell surfaces are typically negative |
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| Bacterial Adherence Mechanisms |
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| • Pili/fimbriae: – mediate initial attachment • S-layers • Capsules • Flagella: – Motility/attachment • Adhesins: – intimate attachment between bacterial/host |
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| Pili (General Features) |
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| • Pilus: – ordered array of single pilin subunits (20 kDa) • Tip of pilus attaches to molecule on host surface – glycoproteins or glycolipids – specialized tip structure • Vary phenotypically – different tip • Expression can be turned on and off “Phase Variation” - Helps with tissue tropism (can stop expression, release and go elsewhere) |
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| Pap (pyelonephritis-associated pili) pili: |
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| – uropathogenic E. coli (UPEC) strains – binds to glycolipids on host cells lining upper urinary tract -Pili binds high number of mannose on the tract (opposite of the norm) -Ascending Urinary tract infection -Gram negative |
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| Type I pili |
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| – binds to mannose-containing host molecules (Mannose within host, exception to generally high mannose seen on pathogens and not host) – all E. coli strains, including UPEC -Gram (-) |
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| Type IV pili |
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| – enteropathogenic E. coli, Vibrio cholerae, Neisseria spp. – Bind to gangliosides (carbohydrates) on host -gram (-) |
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| Curli Pili |
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| – Thin, aggregative pili – diarrhea-producing E. coli strains, Salmonella enteritidis – Bind to fibronectin, laminin, plasminogen -Gram (-) |
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| Tissue tropism and pili expression |
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| • Uropathogenic E. coli – Pap pili and Type I pili– bladder cells • Enteropathogenic E. coli – Type IV pili – intestinal cells |
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| FimH |
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| (Type I pili) binds mannosylated glycoproteins - bladder |
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| PapG |
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| binds gala1-4galb disaccharides - kidney cell glycosphingolipids |
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| FliD |
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| Flagellum as an Adhesin Pseudomonas aeruginosa – FliD mediates attachment to mucin (sticky stuff on top of mucosal layer) -FliD is the Pili tip structure |
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| Adhesins |
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| • Mediate tight adherence • Most pathogens possess many adhesins • Differentially regulated Regulation depends on which stage in infection -Adhesives turned on closer to infection • Often multifunctional |
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| Attachment of adhesin to host cell (effects) |
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| – Signal transduction within the bacterium -Secretion systems infect into host following attachment -Via typeIII (at least in E. coli) – Uptake of the bacterium by the host cell = invasion – Signaling within the host cell |
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| Pseudomonas aeruginosa Adhesion |
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| Type IV Pili - Flagella and FliD Adhesin Attachment induces Type III secretion system Effector proteins • ExoS and ExoT • ExoU and ExoY ExoU: Cleaves phospholipids within plasma membrane within host cell resulting in cell death |
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| ExoS, T, U |
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| -Killing/impairment of phagocytes -Disruption of epithelial/endothelial barriers |
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| ExoS and ExoU |
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| Down regulation of IL-1beta and IL-18 -Will dampen inflammatory response -Pseudomonas aeruginosa lung infections typically lead to other infections of the lung due to this weakening |
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| Neisseria sp |
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| N. gonorrhoeae and N. meningitidis • Pili • Opa Adhesins -Deep invasion allows infection to exist for long and systemic infection |
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| Neisseria Pili (Type IV) - Initial Attachment |
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| PilE – pilin protein N-terminus of protein – conserved (function) C-terminus of protein – hypervariable (invasion) |
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| Opa (Opacity) Adhesins - Result in Tight Adherence |
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| • Family of outer membrane proteins found in N. gonorrhoeae and N. meningitidis • Mediate adherence to epithelial cells, endothelial cells, T lymphocytes, neutrophils |
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| Host Cell Receptors that Opa Attaches To |
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| – Vitronectin, heparin sulfate proteoglycans – CEACAM family (carcinoembryonic antigen cell adhesion molecule) |
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| Neutrophil Opa-CEACAM engagement |
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| Bacteria taken in and killed -Thought to be decoy mechanism |
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| Transcytosis |
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| Movement of bacteria deeper into tissues and through cells -ex. Neisseria: there is attachment to the epithelial layer --> movement through this layer via transcytosis (from OPA and CEACAM engagement at points) --> moves into deeper epithelial layer --> moves through endothelial layer --> can enter blood stream and deseminate through, spreading infection |
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| Invasive Pathogen |
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| Invasion of host cells by intracellular pathogens Tissue invasion by pathogens – Extracellular pathogens -> gain access to deeper tissue by going through cell junction -used by many extracellular pathogens |
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| Facultative Intracellular Bacteria Examples |
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| -Salmonella spp. (typhoid, gastroenteritis) -Yersinia spp. (plague, gastroenteritis) -Listeria monocytogenes (listeriosis) |
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| Extracellular bacteria |
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| -E. coli (gastroenteritis, meningitis) -Streptococcus pyogenes (fasciitis, rheumatic fever) |
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| Overview of Tissue Organization |
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| – Cell junctions – Extracellular matrix (ECM) Connective and Epithelia tissue |
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| General Characteristics of Connective Tissue |
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| -cells sparse -ECM plentiful -cell-cell attachment rare -matrix bears stress |
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| General Characteristics of Epithelial Tissue |
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| -cells plentiful -ECM sparse -cell-cell junctions prevalent -cells bear stress -epithelial layer is tightly packed with not a lot of extracellular tissues; no cushioning |
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| Three Types of Cell Junctions |
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| 1. Occluding 2. Anchoring 3. Communicating -Gap junctions found in every cell and tissue -important for communication, relay electrical impulses and signals, prevalent in places like retina, muscles, etc -open exchange between cells -only allows small cells to pass between them (<1000Da) -signals allow for response to occur within a tissue |
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| Occluding Junctions |
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| Tight Junctions • Seal cells together in epithelium • Selective permeability barriers • Prevent nutrients from diffusing back into lumen • Keep transport proteins and things in place |
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| Occluding Junction Receptors |
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| Apical receptors = faces lumen Basolateral receptors = face bloodstream |
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| How Occluding Junctions Hold Together |
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| -Formed from: claudin and occludins membrane proteins -link with cytoskeletal proteins |
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| Anchoring Junctions |
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| Anchors via cell-cell and cell-matrix Mediate cell-cell and cell-matrix junctions -important for survival -without this interaction, cells will die |
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| Transmembrane adhesion proteins |
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| Adherens junctions and desmosomes •cell-cell junctions •cadherin family Focal adhesions and hemidesmosomes •cell-matrix junctions •integrin family |
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| Intracellular anchor proteins interactions |
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| Adherens junctions and focal adhesions: -talin and vinculin -interact with actin filaments Desmosomes and hemidesmosomes: -plectin -interact with intermediate filaments |
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| Integrins (Function) |
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| Function: • mediate cell-ECM attachment • matrix-cell and cell-matrix signaling -important for survival through contact with matrix, development of cell layers and structure of cell layers |
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| Integrins (Structure) |
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| Structure • a and b subunits (alpha and beta) -9 b subunits -24 a subunits •overlapping recognition -8 integrins bind fibronectin -5 integrins bind laminin Pathogens can mimic these components to allow invasion |
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| Fibronectin |
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| The RGD Region is the cell-binding motif --> aa's R,G,D ; binds integrin molecules Pathogens exploit the RGD motif |
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| Pathogen Exploitation of Anchoring Junctions (E-Cadherin) |
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| Pathogen protein binds to cell-cell anchoring junction protein – binds to E-cadherin -internalin binds e cadherin (cell-cell) – Eg. Yersinia pseudotuberculosis invasin -binds b1 integrins Listeria monocytogenes internalin - binds E-cadherin |
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| Mechanisms used by bacteria to enter cells: INVASION |
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| Trigger -massive disruption and reorganization -membrane ruffling Zipper -not a lot of disruption; invagination, pathogen comes in Opa: binds CEACAM, IntA/A (internalin), Invasin (InvA) etc |
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| Salmonella invasion - SopB |
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| -induces membrane ruffling -activates Rho kinase-dependent actin rearrangement recruits AnnexinA2 -induces actin rearrangement |
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| Salmonella invasion - SopE/E2 |
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| -guanine nucleotide exchange factors -activates Rho GTPases induces actin polymerization and membrane ruffling |
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| Salmonella invasion - SipA/SipC |
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| -bind to actin -inhibits actin depolymerization (SipA) -nucleates actin (SipC) |
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| Salmonella invasion - SptP |
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| -induces actin depolymerization -Does this by removal of inorganic P group --> Inactive GDP |
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| Salmonella invasion - SipB/C (Before SopB) |
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| T3SS pore |
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| Invasive Extracellular Pathogens |
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| Generally, their goal is not to get within a cell; they want to stay extracellular virulence factors allows them to stay extracellular and combat immune response -BUT they do want to get deeper into tissues |
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| Mechanisms of Invasion for Extracellular Pathogens |
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| 1. Exploitation of anchoring junctions – Transcytosis: allows access to deeper epithelium and bloodstream -->also allows access to the lymphatic system -Just like Firbronectin yersinia example 2. Disruption of tight junctions Then they will spread via the bloodstream |
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| Pathogen exploitation of tight junctions |
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| Enteropathogenic E. coli (EPEC) – disrupts tight junctions -causes diarrhea (related to tight junction disruption) |
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| EspF - Effector Protein |
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| • Binds to: Actin, nWASP, Arp2/3 • Causes: – Actin removal from Tight Junction (TJ) – Recruitment of TJ proteins into pedestal • EspF mutant: – No TJ disruption - Smaller pedestals (EspF till needs other effector proteins to work) |
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| What Happens in EspF Mutant? |
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| An EspF mutant (does not express EspF) causes formation of smaller pedestals. THIS IS BECAUSE: -you still get pedestal formation because of Tir, but EspF is needed to get extra movement into the pedestals (ZO proteins wouldn't move) |
