Microbial Disease Causation Criteria
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Which of the following is NOT one of Koch's original postulates?

  • The microorganism must cause disease in healthy animals.
  • The microorganism must be grown in pure culture.
  • The microorganism should have a genetic sequence associated with plant pathogens. (correct)
  • The microorganism must be isolated from lesions of the disease.

    • What is a criterion from Molecular Koch’s Postulates?

  • Inactivation of a gene should enhance pathogenicity.
  • The phenotype should be associated with pathogenic strains. (correct)
  • The microorganism must be able to replicate in soil.
  • Microorganism must always be present in healthy individuals.

    • How does the presence of a pathogen-associated nucleic acid sequence relate to disease prediction?

  • It helps predict the subsequent development of disease. (correct)
  • It is only present in individuals much older than the disease onset.
  • It suggests that the disease is always fatal.
  • It has no correlation with subsequent disease development.

    • Which microorganism cannot be grown in vitro but can infect animals?

    <p>Treponema pallidum</p> Signup and view all the answers

    What does a decrease in copy number of a pathogen-associated nucleic acid sequence indicate?

    <p>A potential resolution of the disease.</p> Signup and view all the answers

    Which of the following diseases is associated with Bartonella henselae?

    <p>Bacillary angiomatosis</p> Signup and view all the answers

    What must happen when a pure culture of a microorganism is inoculated into susceptible animal species?

    <p>Typical disease must result.</p> Signup and view all the answers

    Which of the following statements accurately describes the nature of the pathogen?

    <p>It must have a consistent relationship with the disease's biological characteristics.</p> Signup and view all the answers

    What is the primary function of spores in pathogenic organisms?

    <p>To protect nucleic acids from environmental factors</p> Signup and view all the answers

    Which disease is associated with the pathogen Mycobacterium tuberculosis?

    <p>Tuberculosis</p> Signup and view all the answers

    Through which portal of entry do pathogenic bacteria commonly gain access to the body?

    <p>Respiratory tract</p> Signup and view all the answers

    Which bacterium is primarily transmitted through food and water contamination?

    <p>Vibrio cholerae</p> Signup and view all the answers

    What does bacteremia allow bacteria to do within the body?

    <p>To spread to suitable tissues for multiplication</p> Signup and view all the answers

    What is the significance of IgA in mucous membranes?

    <p>It serves as a primary defense against infection</p> Signup and view all the answers

    What complication can arise from bacteremia due to pneumococcal pneumonia?

    <p>Meningitis</p> Signup and view all the answers

    What is a primary risk factor for the development of pneumonia from pneumococci?

    <p>Absence of antibodies</p> Signup and view all the answers

    What effect does cholera toxin have on the gut?

    <p>It leads to chloride and water flow into the gut lumen.</p> Signup and view all the answers

    Why do bacteria limit their genetic interaction?

    <p>To avoid chromosome disruptions that affect survival.</p> Signup and view all the answers

    What is the process of natural transformation in bacteria?

    <p>DNA from one organism is released and taken up by another.</p> Signup and view all the answers

    What type of genetic element can carry antibiotic resistance genes?

    <p>Transposons.</p> Signup and view all the answers

    What are pathogenicity islands (PAI)?

    <p>Large groups of genes encoding virulence factors.</p> Signup and view all the answers

    Which of the following statements is true regarding plasmids?

    <p>They are extra-chromosomal pieces of DNA capable of replicating.</p> Signup and view all the answers

    How can transposons contribute to genetic diversity in bacteria?

    <p>They move segments of DNA from one part of the genome to another.</p> Signup and view all the answers

    What is the role of bacteriophages in genetic exchange among bacteria?

    <p>They inject phage DNA into bacteria, allowing recombination.</p> Signup and view all the answers

    What role do invasion plasmid antigens (IpA-D) play in Shigella infection?

    <p>They assist in the invasion of mucosal cells.</p> Signup and view all the answers

    Which unusual mechanism do Legionella pneumophila use to infect macrophages?

    <p>Coiling phagocytosis</p> Signup and view all the answers

    What is the primary function of the B subunit in exotoxins?

    <p>To facilitate adherence of the toxin complex to the host cell.</p> Signup and view all the answers

    Which bacteria is associated with the production of diphtheria toxin?

    <p>Corynebacterium diphtheriae</p> Signup and view all the answers

    What is the primary mode of action for endotoxins?

    <p>They are lipid molecules found in the bacterial cell membrane.</p> Signup and view all the answers

    How do Neisseria gonorrhoeae adhere to host cells during infection?

    <p>Through the use of pili and Opa proteins.</p> Signup and view all the answers

    What are toxoids used for in medicine?

    <p>As vaccines formed from modified toxins.</p> Signup and view all the answers

    Which type of bacteria can use internalins to assist in their engulfment by host cells?

    <p>Listeria monocytogenes</p> Signup and view all the answers

    What is the primary effect of theta toxin produced by Clostridia and Staphylococcus aureus?

    <p>It has a necrotizing effect.</p> Signup and view all the answers

    What characterizes Toxic Shock Syndrome caused by TSST-1?

    <p>Shock, high fever, and diffuse red rash.</p> Signup and view all the answers

    How does the enterotoxin from Vibrio cholerae affect the intestinal cells?

    <p>It increases adenylate cyclase activity, leading to cAMP increase.</p> Signup and view all the answers

    What is the most common source of Staphylococcal enterotoxin that causes food poisoning?

    <p>Improperly refrigerated meat and dairy.</p> Signup and view all the answers

    What is a significant pathophysiologic effect of lipopolysaccharides (LPS) in the bloodstream?

    <p>They bind to circulating proteins and activate immune response.</p> Signup and view all the answers

    Which toxin acts similarly to TSST-1 and results in scarlet fever?

    <p>Pyrogenic exotoxin A from Group A streptococci.</p> Signup and view all the answers

    What role do the subunits of Vibrio cholerae toxins play in affecting intestinal function?

    <p>Subunit B binds to microvilli, initiating toxin activity.</p> Signup and view all the answers

    Which of the following is true about endotoxins in Gram-negative bacteria?

    <p>They consist of heat-stable lipooligosaccharides.</p> Signup and view all the answers

    Study Notes

    Microbial Disease Causation Criteria

    • Koch's Postulates outline essential conditions to establish a microorganism's role in disease.
    • Isolation of a microorganism must occur in all disease cases and correlate with observed lesions.
    • The microorganism should be culturable in pure form outside the host for multiple generations.
    • Inoculation of the pure culture in susceptible animals must reproduce the disease.
    • Re-isolation of the microorganism from lesions in experimentally induced disease is necessary.

    Molecular Koch’s Postulates

    • Pathogenic strains should exhibit a significant association with specific phenotypes.
    • Specific gene inactivation must result in reduced virulence or pathogenicity.
    • Restoration of pathogenicity should occur upon reverting mutated genes to wild-type.

    Molecular Guidelines for Causation

    • Pathogen nucleic acid should be found in tissue sites with pathology but absent in most healthy controls.
    • Presence of nucleic acid should decrease with disease resolution and increase with recurrence.
    • Predictive marker for disease development found in healthy subjects.
    • The pathogen's characteristics should match known profiles of related organisms.

    Disease Examples

    • Whipple disease caused by Tropheryma whipplei.
    • Bacillary angiomatosis linked to Bartonella henselae.
    • Human monocytic ehrlichiosis associated with Ehrlichia chaffeensis.
    • Hanta virus pulmonary syndrome from Sin Nombre virus.
    • Kaposi sarcoma related to Human herpesvirus 8.

    Limitations of Koch’s Postulates

    • Some pathogens, like Treponema pallidum (syphilis) and Mycobacterium leprae (leprosy), cannot be cultured in vitro.
    • Spores can protect microbial nucleic acids from environmental stressors and promote survival until germination.

    Transmission and Contamination

    • Water and food contamination examples include Vibrio cholera and Escherichia coli, leading to diarrhea.
    • Mycobacterium tuberculosis leads to respiratory disease.
    • Staphylococcus aureus can be transmitted from person to person via hands.

    Portals of Entry for Pathogenic Bacteria

    • Pathogens enter through mucous membranes of skin, respiratory, gastrointestinal, genital, and urinary tracts.
    • IgA serves as a primary defense against infections at these entry sites.

    The Infectious Process

    • Infection begins with adherence to host cells, followed by proliferation through bodily tissues or the lymphatic system.
    • Bacteremia allows pathogens to spread and infect multiple sites (e.g., pneumococcal pneumonia).

    Pathogen Survival and Genetic Exchange

    • Bacteria are haploid and limit genetic interactions to ensure survival in specific environments.
    • Mechanisms of genetic exchange include natural transformation (uptake of environmental DNA), plasmids, transposons, and bacteriophages.

    Pathogenicity Islands (PAIs)

    • PAIs are clusters of virulence genes that originate from gene transfers and do not replicate independently.
    • Notable examples of bacteria utilizing PAIs include Shigella and Listeria monocytogenes.

    Toxins

    • Exotoxins, produced by both gram-positive and gram-negative bacteria, can induce disease; endotoxins are part of the cell membrane.
    • Exotoxins consist of two subunits: B subunit (adherence) and A subunit (toxic activity).

    Specific Toxin Examples

    • Corynebacterium diphtheriae produces diphtheria toxin, leading to diphtheria.
    • Staphylococcus aureus produces Toxic Shock Syndrome Toxin-1 (TSST-1), causing toxic shock syndrome.
    • Enterotoxins linked to diarrheal diseases are produced by Vibrio cholerae, leading to severe dehydration symptoms.

    Endotoxins

    • Endotoxins, such as lipopolysaccharides (LPS) from gram-negative bacteria, are released when bacteria lyse and can cause systemic effects like sepsis.
    • LPS binds proteins in the bloodstream and interacts with immune cells contributing to inflammatory responses.

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    Description

    Explore the essential criteria for establishing the role of microorganisms in disease causation. This quiz covers Koch's Postulates as well as Molecular Koch’s Postulates, emphasizing the importance of pathogen characteristics and experimental validation. Test your knowledge on the foundational principles of microbiology and pathogenicity.

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