Unit 3 Exam Study Guide

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Important Concepts in Microbiology

Key Vocabulary

This section introduces essential terms for understanding infectious diseases, immunity, and epidemiology in microbiology.

Communicable disease: An illness that can be transmitted from one person to another.
Contagious disease: A communicable disease that spreads easily and rapidly among individuals.
Endemic disease: A disease regularly found among particular people or in a certain area.
Epidemic disease: A sudden increase in the number of cases of a disease above what is normally expected.
Pandemic disease: An epidemic that has spread over several countries or continents, affecting a large number of people.
Koch's postulates: Criteria used to establish a causative relationship between a microbe and a disease.
Nosocomial infection: An infection acquired in a hospital or healthcare facility.
Vehicle: A nonliving medium (such as water, food, or air) that can transmit infectious agents.
Airborne/Foodborne: Modes of disease transmission via air or food, respectively.
Vector: An organism, typically an insect, that transmits a pathogen from one host to another.
Reservoir: The natural habitat of a pathogen where it lives and multiplies.
Transmission: The mechanism by which a pathogen spreads from one host to another.
Exotoxin/Endotoxin: Toxins produced by bacteria; exotoxins are secreted, endotoxins are part of the bacterial cell wall.
Cytokine: Small proteins important in cell signaling, especially in immune responses.
Complement: A group of proteins that enhance immune responses.
Opsonization: The process by which pathogens are marked for ingestion and destruction by phagocytes.
Inflammation: The body's response to infection or injury, characterized by redness, heat, swelling, and pain.
Phagocytosis: The process by which cells (e.g., macrophages, neutrophils) engulf and digest pathogens.
Symbiosis: Interaction between two different organisms living in close physical association.
Mutualism: Both organisms benefit from the relationship.
Parasitism: One organism benefits at the expense of the other.
Commensalism: One organism benefits, the other is unaffected.
Macrophage/Neutrophil/Basophil/Eosinophil/Monocyte/Lymphocyte: Types of white blood cells involved in immune responses.
Active immunity: Immunity resulting from the production of antibodies by the immune system in response to the presence of an antigen.
Passive immunity: Immunity acquired by the transfer of antibodies from another individual.
Acquired immunity: Immunity developed during an individual's lifetime, either through infection or vaccination.
Antibody: A protein produced by B cells that binds to specific antigens.
Immunity: The ability of an organism to resist infection.
Innate immunity: Non-specific defense mechanisms present from birth.
Exposure: Contact with a pathogen.
Interferon: Proteins released by host cells in response to pathogens, especially viruses.
Major histocompatibility complex (MHC): Proteins on cell surfaces important for immune recognition.
Pattern recognition receptor (PRR): Receptors that recognize common patterns in pathogens.
Epitope: The specific part of an antigen recognized by antibodies.
Phagocytosis: The ingestion of bacteria or other material by phagocytes.
Variation: Differences in genetic or phenotypic traits.
Immunoglobulin: Another term for antibody.
Antigenic shift/Antigenic drift: Mechanisms by which viruses change their surface proteins to evade immune detection.

Koch's Postulates and Disease Causation

Koch's Postulates

Koch's postulates are a set of criteria used to establish a causative link between a specific microorganism and a disease. They have been fundamental in the development of microbiology and the understanding of infectious diseases.

The microorganism must be found in all organisms suffering from the disease, but not in healthy organisms.
The microorganism must be isolated from a diseased organism and grown in pure culture.
The cultured microorganism should cause disease when introduced into a healthy organism.
The microorganism must be re-isolated from the experimentally infected host and identified as being identical to the original specific causative agent.

Contribution: These postulates helped establish the germ theory of disease and are still used, with modifications, in modern microbiology.

Transmission and Epidemiology

Modes of Transmission

Understanding how diseases spread is crucial for controlling outbreaks and preventing infection.

Direct contact: Physical transfer of pathogens between individuals.
Indirect contact: Transfer via contaminated objects (fomites).
Vehicle transmission: Spread through air, water, or food.
Vector transmission: Spread by insects or animals.

Example: Hepatitis B can be transmitted via contaminated syringes (vehicle transmission).

Reservoirs and Vectors

Reservoir: The natural source of a pathogen (e.g., humans, animals, environment).
Vector: An organism that transmits pathogens (e.g., mosquitoes for malaria).

Types of Diseases

Classification

Symptomatic disease: Disease with observable symptoms.
Asymptomatic disease: Disease without noticeable symptoms.
Primary infection: Initial infection by a pathogen.
Secondary infection: Subsequent infection by a different pathogen.
Local infection: Confined to a specific area.
Systemic infection: Spread throughout the body.

Immunity and Immune Responses

Innate vs. Adaptive Immunity

The immune system protects the body from pathogens through two main mechanisms: innate and adaptive immunity.

Innate immunity: Non-specific, immediate defense present from birth (e.g., skin, phagocytes).
Adaptive immunity: Specific, acquired defense that develops after exposure to antigens (e.g., antibodies, lymphocytes).

Active and Passive Immunity

Active immunity: Produced by the host's own immune system after exposure to an antigen (natural infection or vaccination).
Passive immunity: Acquired by receiving antibodies from another source (e.g., maternal antibodies, immunoglobulin therapy).

Antibodies and Immunoglobulins

Antibodies are proteins produced by B cells that specifically bind to antigens.

Structure: Antibodies consist of two heavy chains and two light chains, forming a Y-shaped molecule.
Genetic diversity: Antibody diversity is generated by gene rearrangement and somatic hypermutation.
Classes: Immunoglobulins are classified into IgG, IgM, IgA, IgE, and IgD.

Example: Secretory IgA is found in mucosal areas and provides protection against pathogens.

Antigenic Variation

Antigenic drift: Small genetic changes in pathogens (e.g., influenza virus) that alter surface proteins.
Antigenic shift: Major genetic changes resulting in new surface proteins, often leading to pandemics.

Cells of the Immune System

White Blood Cells

Different types of white blood cells play distinct roles in immune defense.

Neutrophils: Phagocytic cells that respond quickly to infection.
Macrophages: Engulf and digest pathogens; present antigens to T cells.
Basophils: Release histamine during allergic reactions.
Eosinophils: Combat parasitic infections.
Monocytes: Differentiate into macrophages and dendritic cells.
Lymphocytes: Include B cells (produce antibodies) and T cells (cell-mediated immunity).
NK cells: Destroy virus-infected and cancerous cells.
Dendritic cells: Present antigens and activate T cells.

Immunological Techniques and Testing

Serology and Immunoassays

Laboratory techniques are used to detect antigens or antibodies in blood samples.

Serology: The study and diagnostic identification of antibodies in serum.
Immunology: The study of the immune system and immune responses.
Viral hemagglutination inhibition: A test to detect antibodies that prevent viruses from agglutinating red blood cells.

Example: At-home pregnancy tests detect human chorionic gonadotropin (hCG) using immunoassay technology.

Major Historical Figures

Edward Jenner

Edward Jenner is known for developing the first successful vaccine (smallpox) using cowpox virus, laying the foundation for modern immunology.

Typhoid Mary

"Typhoid Mary" (Mary Mallon) was an asymptomatic carrier of Salmonella typhi who spread typhoid fever, highlighting the importance of carriers in disease transmission.

Sample Table: Comparison of Immunity Types

Type of Immunity	Source	Duration	Example
Active Natural	Infectious	Long-term	Recovery from measles
Active Artificial	Vaccination	Long-term	MMR vaccine
Passive Natural	Maternal antibodies	Short-term	Antibodies in breast milk
Passive Artificial	Injection of antibodies	Short-term	HRIG for rabies exposure

Additional info:

Some terms and explanations have been expanded for clarity and completeness.
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