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Microbiology: Infection, Immunity & Vaccines

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  • True Pathogens

    Microorganisms that can cause disease in healthy individuals.

  • Opportunistic Pathogens

    Normally harmless microbes that cause disease when the host's immunity is weakened or when they enter unusual body sites.

  • Normal Biota (Flora)

    Microorganisms that normally inhabit the body without causing disease but can sometimes cause endogenous infections.

  • Infectious Dose (ID)

    The minimum number of microbes required to establish an infection.

  • Communicable Disease

    Diseases that can be transmitted from one host to another.

  • Contagious Disease

    Highly communicable diseases that spread easily, such as measles.

  • Non-Communicable Disease

    Diseases that cannot be transmitted between individuals, e.g., tetanus.

  • Nosocomial Infections

    Infections acquired in healthcare settings, often due to weakened immunity or exposure to pathogens.

  • Virulence Factors

    Microbial components that enhance the ability to cause disease, such as fimbriae, capsules, coagulase, and leukocidins.

  • Symptoms vs. Signs

    Symptoms are subjective experiences felt by the patient; Signs are objective observations measurable by others.

  • Reservoir

    The natural habitat where a pathogen normally lives, such as humans, animals, or soil.

  • Direct Transmission

    Person-to-person contact spreading disease.

  • Indirect Transmission

    Spread of disease via contaminated objects (fomites), food, water, or air.

  • Vector

    A living organism, often an insect, that transmits disease (e.g., mosquitoes for malaria).

  • Mutualism

    A symbiotic relationship where both organisms benefit.

  • Endotoxins

    Produced by Gram-negative bacteria; consist of lipopolysaccharide (LPS) released when cells die; cause fever and inflammation.

  • First Line of Defense in Innate Immunity

    Physical and chemical barriers like skin, mucous membranes, lysozyme, and stomach acid that prevent pathogen entry.

  • Four Classic Signs of Inflammation

    Rubor (redness), Calor (heat), Tumor (swelling), Dolor (pain).

  • Phagocytosis Steps

    Chemotaxis, engulfment, phagolysosome formation, and destruction of the pathogen.

  • Key Cells of Innate Immunity

    Neutrophils (first responders), macrophages (engulf pathogens and present antigens), and leukocytes (white blood cells).

  • Complement System Function

    Enhances inflammation, attracts phagocytes, and destroys pathogens.

  • Difference Between Induced and Non-Specific Defenses

    Non-specific defenses are always present; induced defenses activate after infection (e.g., inflammation, fever).

  • B Cells vs. T Cells

    B Cells produce antibodies (humoral immunity); T Cells attack infected or abnormal cells directly (cell-mediated immunity).

  • MHC I vs. MHC II

    MHC I is on all nucleated cells and presents antigens to cytotoxic T cells; MHC II is on antigen-presenting cells and presents to helper T cells.

  • Antibody Neutralization

    Antibodies block toxins or viruses to prevent infection.

  • Primary vs. Secondary Immune Response

    Primary is the first exposure with slow response and IgM production; secondary is faster and stronger with IgG dominance due to memory cells.

  • IgM Antibody

    First antibody produced during infection.

  • IgG Antibody

    Most abundant antibody; provides long-term immunity and crosses the placenta.

  • Types of Vaccines

    Attenuated (live, weakened) vaccines provide strong immunity but are unsafe for immunocompromised; inactivated (killed) vaccines are safer but may require boosters.

  • Clonal Deletion

    Removal of self-reactive lymphocytes to prevent autoimmune disease.