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    Microbial Pathogenesis: Amin - Bakir@hmu - Edu.krd

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    Asma Muhammed majeed
    This document discusses microbial pathogenesis and the mechanisms by which microbes cause infection. It explains that microbes have developed virulence factors and mechanisms to infect hosts through various entry points like mucous membranes, skin, or parenterally. Key virulence factors that help microbes infect hosts include adherence factors, cell wall components, enzymes, toxin production, and the ability to evade host immune defenses. Microbes can damage tissues through enzymes or toxins. Exotoxins are soluble toxins released by microbes while endotoxins are part of the cell walls of gram-negative bacteria.

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    Microbial Pathogenesis: Amin - Bakir@hmu - Edu.krd

    Uploaded by

    Asma Muhammed majeed
    28 views16 pages
    This document discusses microbial pathogenesis and the mechanisms by which microbes cause infection. It explains that microbes have developed virulence factors and mechanisms to infect hosts through various entry points like mucous membranes, skin, or parenterally. Key virulence factors that help microbes infect hosts include adherence factors, cell wall components, enzymes, toxin production, and the ability to evade host immune defenses. Microbes can damage tissues through enzymes or toxins. Exotoxins are soluble toxins released by microbes while endotoxins are part of the cell walls of gram-negative bacteria.

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    LG2-Pathogenesis

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    This document discusses microbial pathogenesis and the mechanisms by which microbes cause infection. It explains that microbes have developed virulence factors and mechanisms to infect hosts through various entry points like mucous membranes, skin, or parenterally. Key virulence factors that help microbes infect hosts include adherence factors, cell wall components, enzymes, toxin production, and the ability to evade host immune defenses. Microbes can damage tissues through enzymes or toxins. Exotoxins are soluble toxins released by microbes while endotoxins are part of the cell walls of gram-negative bacteria.

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    © All Rights Reserved
    Download as PPTX, PDF, TXT or read online from Scribd
    Download as pptx, pdf, or txt
    28 views16 pages

    Microbial Pathogenesis: Amin - Bakir@hmu - Edu.krd

    Uploaded by

    Asma Muhammed majeed
    This document discusses microbial pathogenesis and the mechanisms by which microbes cause infection. It explains that microbes have developed virulence factors and mechanisms to infect hosts through various entry points like mucous membranes, skin, or parenterally. Key virulence factors that help microbes infect hosts include adherence factors, cell wall components, enzymes, toxin production, and the ability to evade host immune defenses. Microbes can damage tissues through enzymes or toxins. Exotoxins are soluble toxins released by microbes while endotoxins are part of the cell walls of gram-negative bacteria.

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    of 16

    Microbial

    Pathogenesis
    Dr. Amin Aziz Bakir
    College of Medicine – HMU
    amin.bakir@hmu.edu.krd
    Microbial Pathogenesis
    - Microbial pathogenesis is the ability of microbes, or their
    components, to cause infection in a host
    - It is a complex mode of interactions between hosts and pathogens

    - During the long course of evolution, disease-causing pathogenic


    microbes have developed a variety of virulence mechanisms and
    virulence encoding factors or genes having inducible or constitutive
    expression patterns
    The Pathogenicity
    The degree of pathogenesis caused by the
    interaction of microbe – host and determined by:
    1. The virulence factors
    2. Intrinsic mechanisms
    o The number of microbial entities that are administered
    in the host system
    o The route of transmission

    o Host specific defense mechanisms


    Microbial Mechanisms of Pathogenicity
    Entry into the Host
    The three main portals of entry are:
    • Mucous membranes
    • Skin
    • Parenteral
    Mucous Membranes
    Epithelial tissue lining the:
    - Respiratory tract: Easiest and most frequently used entry
    site for microbes
    - Gastrointestinal tract: Another common entry site.
    - Entry occurs through water, food, contaminated fingers and fomites
    - Must survive stomach HCl, enzymes, and bile
    - Genitourinary tract: Entry site for most sexually transmitted
    diseases (STDs)
    - Conjunctiva: Membrane covering eyes and eyelids
    The Skin

    • Unbroken skin is impenetrable by most


    microbes
    • Some microbes gain access through hair
    follicles and sweat glands.
    • Some parasites can penetrate through
    intact skin
    • Certain fungi (dermatophytes) grow on skin Cutaneous larva (creeping
    and produce enzymes that break down eruption) by sandworm
    keratin
    Parenteral route

    Microbes are deposited directly into the tissues beneath the skin
    or mucous membranes
    - Injections

    - Bites
    - Cuts & injuries

    - Wounds
    - Punctures and splitting due to swelling or drying
    Preferred Portal of Entry
    Many microbes have a preferred
    portal of entry which is a prerequisite
    to cause disease

    Example: Streptococcus pneumoniae


    that are inhaled can cause pneumonia
    But, if swallowed cause less severe
    diseases
    Virulence Factors
    - Play a crucial role in microbial growth at elevated temperatures

    - Promote the adherence, penetration, and dissemination into


    their host
    - Pathogenic resistance against immune defense:
    - Complement system
    - Phagocytosis
    - Providing evasion from adaptive immune responses
    - Nutritional or metabolic factors

    - Necrotic factors

    - Causing variations in phenotypic morphology


    Adherence

    Attachment of microbe to host tissue requires:


    - Adhesins or Ligands: Surface molecules on pathogen that
    bind specifically to host cell surface molecules.
    - Can be found on glycocalyx, fimbriae, viral capsid, or
    other surface structure.
    - Receptors: Surface molecules on host tissues to which
    pathogen adhesions bind
    Cell Wall Components

    M protein: Found on cell surface and fimbriae of Streptococcus


    pyogenes. Mediates attachment and helps resist phagocytosis

    Waxes: In cell wall of Mycobacterium tuberculosis helps resist


    digestion after phagocytosis

    Lipopolysaccharide (LPS): causing macrophages to release


    interleukin-1 which is carried to hypothalamus (temperature
    control center) resulting in fever.
    Enzymes
    Lyse cells, form or dissolve clots, and dissolve materials in tissue.
    - Leukocidins: Destroy white blood cells that are phagocytes
    - Hemolysins: Destroy red blood cells
    - Coagulases: Produce blots in blood
    - Bacterial Kinases: Break down clots produced by body to isolate
    infection
    - Hyaluronidase: Breaks down hyaluronic acid which holds cells
    together in connective tissue
    - Collagenase: Breaks down collagen which forms connective tissue of
    muscles, skin, and other organs
    - Necrotizing Factors: Kill host cells
    - Hypothermic factors: Decrease body temperature
    - Lecithinase: Destroys plasma membrane of cells
    - Proteases: Break down proteins in tissue
    Toxin production
    - Toxins: Poisonous substances produced by microbes
    - Frequently toxins are the main pathogenic factor
    - Toxigenicity: Ability of a microbe to produce toxins
    - Toxemia: Presence of toxins in the blood
    - Toxin effects: May include fever, cardiovascular problems,
    diarrhea, shock, destruction of red blood cells and blood vessels,
    and nervous system disruptions.
    - Of 220 known bacterial toxins, 40% damage euokaryotic cell
    membranes
    - Two types of toxins:
    Exotoxins
    Endotoxins
    Exotoxins
    - Produced mainly by Gram-positive bacteria

    - Soluble in body fluids, rapidly transported throughout the body

    - Most genes for toxins are carried on plasmids or phages

    - Produced inside bacteria and released into host tissue

    - Responsible for disease symptoms and/or death:


    - Cytotoxins: Kill or damage host cells
    - Neurotoxins: Interfere with nerve impulses
    - Enterotoxins: Affect lining of gastrointestinal tract
    - Toxoids: Toxins that have been altered by heat or chemicals. Can be
    used as vaccines for diphtheria and tetanus.
    Endotoxin
    - Part of outer membrane surrounding Gram-negative bacteria
    - Effect exerted when gram-negative cells die and cell walls
    undergo lysis, liberating endotoxin
    - Causes similar signs and symptoms:
    • Chills, fever, weakness, general aches, blood clotting,
    tissue death, shock, and even death.
    • Can induce miscarriage
    • Fever: Pyrogenic response

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