209 12-02-24
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Questions and Answers

What is the primary role of Shiga toxin in E. coli O157/H7 pathogenesis?

  • Promotes bacterial replication without causing harm
  • Inhibits the bacterium's ability to attach to host cells
  • Causes host damage and facilitates growth of the pathogen (correct)
  • Enhances immune response against the bacterium

    • What mechanism allows E. coli O157/H7 to acquire the Shiga toxin gene from Shigella?

  • Genetic mutation within the E. coli genome
  • Vertical gene transfer during reproduction
  • Spontaneous plasmid transformation
  • Horizontal gene transfer (correct)

    • What primarily characterizes pathogenicity islands in pathogens?

  • Regions of the genome that enhance the host immune response
  • Unique nucleotide sequences non-existent in other organisms
  • Clusters of genes that dictate virulence factors (correct)
  • Segments of DNA that resist antibiotic treatments

    • Which component do enveloped viruses use to bind to their host cell receptors?

    <p>Glycoproteins in the viral envelope (C)</p> Signup and view all the answers

    Which of the following best describes viral infection specificity?

    <p>Viruses exhibit tissue tropism and specific host range (A)</p> Signup and view all the answers

    What structure do bacteria primarily use for adherence to host cells?

    <p>Fimbriae, with specific binding proteins (A)</p> Signup and view all the answers

    Which of the following processes is essential for pathogens to evade host defenses?

    <p>Dodging immune detection by mimicking host surface proteins (D)</p> Signup and view all the answers

    What is an essential step that pathogens must undertake after causing damage to the host?

    <p>Exit to transmit the infection to a new host (C)</p> Signup and view all the answers

    What mechanism does the cholera toxin utilize to induce diarrhea?

    <p>It binds to GM1 ganglioside and increases cAMP levels. (D)</p> Signup and view all the answers

    Which component of enterotoxigenic E.coli is similar to cholera toxin?

    <p>Labile toxin (LT) (C)</p> Signup and view all the answers

    How do super antigens contribute to a systemic inflammatory response?

    <p>By activating a high proportion of helper T cells. (C)</p> Signup and view all the answers

    What effect do endotoxins have on host immune cells?

    <p>Promote immune cell activation and cytokine secretion. (C)</p> Signup and view all the answers

    What is the role of alpha toxin in bacterial pathogenesis?

    <p>To form pores in host cell membranes. (D)</p> Signup and view all the answers

    What is characteristic of A-B type toxins?

    <p>They are comprised of A and B subunits, where B binds to host cells. (B)</p> Signup and view all the answers

    Which type of bacterial structure aids in the adherence of Vibrio cholerae to intestinal cells?

    <p>Fimbriae (A)</p> Signup and view all the answers

    What is a significant consequence of increased levels of cAMP due to cholera toxin in enterocytes?

    <p>Activation of chloride channels leading to water secretion. (C)</p> Signup and view all the answers

    What is the primary function of the protein at the tip of the pili?

    <p>To mediate adherence to host cells (D)</p> Signup and view all the answers

    Which type of pili is characterized by its ability to extend and retract dynamically?

    <p>Type IV pili (B)</p> Signup and view all the answers

    What distinguishes exotoxins from endotoxins?

    <p>Exotoxins are secreted by living pathogens, whereas endotoxins are released from dead bacteria (A)</p> Signup and view all the answers

    Which bacterial adhesin is known to bind host cell integrins?

    <p>Pertactin (D)</p> Signup and view all the answers

    What role do biofilms play in bacterial pathogenesis?

    <p>They provide nonspecific adherence and protect against immune response (A)</p> Signup and view all the answers

    Which secretion system allows bacteria to inject virulence factors directly into host cells?

    <p>Type III secretion system (B)</p> Signup and view all the answers

    What is the primary purpose of Type I pili in bacteria?

    <p>Binding to specific sugars on host cells (B)</p> Signup and view all the answers

    How do pathogens generally achieve growth and persistence in the host?

    <p>Through the production of toxins that interfere with host cell function (D)</p> Signup and view all the answers

    Flashcards

    Pathogen definition

    A pathogen is an organism that causes disease.

    Pathogen traits

    Pathogens need entry, adherence (attachment), avoidance of host defenses, growth, and exit to successfully infect.

    Pathogen origin

    Pathogens can originate from other organisms, acquiring virulence genes through horizontal gene transfer.

    Virulence factor location

    Virulence factors, like toxins, often group in clusters called pathogenicity islands within the genome of a microorganism.

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    Bacterial attachment

    Pili (fimbriae), bacterial surface proteins with adhesins, mediate attachment to host cells.

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    Viral attachment

    Enveloped viruses use glycoproteins in their envelope, while non-enveloped viruses use capsid proteins to attach to host cells.

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    Shiga toxin role

    Shiga toxin from Shigella causes damage in E. coli O157/H7 infections.

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    Horizontal gene transfer

    Horizontal gene transfer is the process by which one organism gives genetic material to another organism.

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    A-B toxin structure

    A toxin composed of two subunits: a B subunit that binds to the host cell and an A subunit that causes damage inside the cell.

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    Cholera toxin

    A toxin produced by Vibrio cholerae that causes diarrhea by increasing levels of cyclic AMP in the intestine.

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    Enterotoxin

    A toxin affecting the small intestine, causing diarrhea.

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    Hemolysin

    A toxin that damages cell membranes, often by creating pores.

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    Shiga toxin

    An A-B toxin that stops protein synthesis in cells.

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    Superantigen

    A toxin that activates many T cells, triggering an excessive immune response.

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    Endotoxin

    A toxin, typically composed of LPS, released from Gram-negative bacteria.

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    Sepsis

    Serious, potentially life-threatening condition stemming from a blood-borne bacterial infection.

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    Bacterial pili

    Protein fibers on bacterial surfaces that allow attachment to host cells.

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    Type I pili

    Fixed bacterial pili that bind specific sugars on host cells.

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    Type IV pili

    Dynamic bacterial pili that extend and retract for attachment.

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    Non-pili adhesins

    Bacterial proteins that attach to host cell proteins for contact.

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    Biofilms

    Bacterial communities that create a protective matrix for adherence.

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    Bacterial secretion systems

    Mechanisms bacteria use to deliver virulence factors to host cells.

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    Study Notes

    Pathogens

    • Pathogens are microorganisms that cause disease
    • Successful pathogens must accomplish entry, adherence, avoidance, growth, and exit.

    Pathogenesis Overview

    • Entry: Pathogens attach to the host using specific receptors, determining the initial infection site.
    • Adherence: Pathogens must attach to their host. Special receptors determine the site of infection.
    • Avoidance: Pathogens must avoid the host's defenses; rapid immune responses will eliminate them before they can replicate.
    • Growth: Growth is linked to host damage.
    • Exit: Transmission to a new host is the final stage.

    Pathogen Virulence Factors

    • Pathogens acquire virulence genes (e.g., for toxins and adhesins) through horizontal gene transfer.
    • These genes are often clustered on 'pathogenicity islands', distinguishable by different G-C base-pair content from the surrounding genome.
    • For example, E. coli O157/H7 acquired a Shiga toxin gene from Shigella, making it pathogenic.

    Pathogen Attachment

    • Bacterial structures: Pili (fimbriae) are surface proteins with attachment subunits (adhesins). Different species have different pili, binding to host cell carbohydrate structures.

      • Pili tip proteins determine binding specificity.
      • Type I pili, capped with FimH, bind mannose on intestinal epithelium.
      • Type I pili, capped with PapG, bind digalactose on urinary tract epithelium.
      • Type IV pili are dynamic, extending and retracting to pull bacteria close to host cell membranes.

    • Non-pili adhesins: These are distinct bacterial surface proteins that bind to host cell proteins used for cell-to-cell contact.

      • Example: Bacterial Pertactin binds host cell integrins.
      • Streptococcal M protein also acts as an adhesin.

    Biofilms

    • Most organisms live in biofilms.
    • Coordinate production of extracellular polysaccharide (EPS) forms a highly adhesive matrix.
    • Biofilms create barriers that block immune mediators.
    • Biofilms contribute to infections: oral, lung, bladder; and pose problems for in-dwelling medical devices.

    Toxin Production

    • Pathogen growth relies on toxins that disrupt host cell function or lead to cell death.

    • Exotoxins: Secreted by pathogens.

    • Endotoxins: Released from dead Gram-negative pathogens.

    • Types of toxins:

      • Membrane disruption: Examples include alpha-toxin, a hemolysin.
      • Inhibiting protein synthesis: Example includes Shiga toxin.
      • Disrupting signal transduction: Example is Cholera toxin
      • Cell cycle disruption: Example is cytolethal distending toxins.

    Type III and Type II Secretion Systems

    • Bacteria employ secretion mechanisms to deliver virulence factors.
    • Type III systems directly inject factors into host cells.
    • Type II systems secrete factors into the extracellular environment.

    A-B Toxin Structure

    • Many toxins have an A-B structure:
      • B subunit binds host cell surface.
      • A subunit exerts toxic effect inside the cell after transport

    Cholera Toxin

    • Vibrio cholerae secretes cholera toxin (a very similar toxin is also made by Entertoxigenic E. coli).
    • This toxin causes diarrhea.
    • It induces chloride secretion by activating a chloride channel and disrupting nutrient uptake.
    • It binds to GM1 ganglioside of intestinal cells. The released A subunit triggers a CAMP increase, activating a chloride channel, which increases ion secretion and diarrhea.

    Sepsis

    • Sepsis is a serious, blood-borne bacterial infection.
    • Mortality from sepsis is high (17%) compared to other conditions (2%).
    • Rapid diagnosis is critical for survival.
    • Incidence of sepsis is increasing with population aging.

    Microbial Pathogen Life Styles and Immune Responses

    • Microbial pathogens have diverse life styles (extracellular, intracellular).
    • Whatever the lifestyle, pathogens avoid or block the host immune response to be successful.

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    Related Documents

    Pathogen Structures & Mechanisms PDF

    Description

    Explore the fascinating world of pathogens in this quiz. Learn about their entry, adherence, immune avoidance, growth, and exit strategies. Understand the role of virulence factors and how they contribute to disease causation.

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