Microbes: Human Interaction

Relationships between Microbes and Their Hosts

  • The human body exists in a state of dynamic equilibrium.

  • Many interactions between microbes and hosts involve the development of biofilms.

  • Colonization of the body involves a constant process of "give and take".

  • Example: Normal microbiota.

Initial Colonization of the Newborn

  • Table 14.2: Microbiota and Humans

    • Location of Microbiota: Specific sites in the body.

    • Where Microbiota Are Not Found: Certain sterile sites within the body.

    • Environments and Associated Species: Different environmental niches host distinct microbial communities.

    • Impact of Microbiota: The effect that microbiota have on human health and development.

Fundamental Events in Pathogenesis

  • Stages of Pathogenesis: Includes several key events that define how infections occur:

    1. Portal of Entry: Route through which pathogens enter the host.

    2. Adherence: The ability of a microbe to attach to host tissues.

    3. Penetration/Invasion: The process of moving into deeper tissues.

    4. Proliferation: Increase in the number of pathogens within host tissues.

    5. Pathology: Results from infection of target tissues and the resulting disease.

    6. Portal of Exit: Exit routes for the pathogen from the host.

  • Requirement for an Infectious Dose (ID):

    • Definition: The minimum number of microbes required for infection to proceed.

    • Microbes that have smaller IDs typically exhibit greater virulence.

    • If ID is not reached, infection will not occur.

Surviving Host Defenses

  • Initial Response: The host's defenses first respond through phagocytes.

  • Antiphagocytic Factors: Mechanisms utilized by pathogens to evade phagocytosis.

    • Examples:

    • Certain species of Staphylococcus and Streptococcus produce leukocidins, which are toxic to white blood cells.

    • Production of slime layers or capsules that inhibit phagocytosis.

    • Ability to survive within phagocytes (intracellular phagocytosis).

Stages in the Course of Infection and Disease

  • Signs and Symptoms of Inflammation: Initial effects observed during infection due to immune activation:

    • Symptoms include fever, pain, soreness, and swelling.

  • Signs of Inflammation:

    • Edema: Accumulation of fluid in tissues.

    • Granulomas and Abscesses: Walled-off collections of inflammatory cells and microbes.

    • Lymphadenitis: Swelling of lymph nodes due to inflammation.

Signs of Infection in the Blood

  • Changes in White Blood Cell Counts: Indicators of infection severity and type.

    • Leukocytosis: Increase in the number of white blood cells (WBCs).

    • Leukopenia: Decrease in the number of WBCs.

  • Types of Bacteremia and Viremia:

    • Septicemia: Presence of multiplying microorganisms in the blood.

    • Bacteremia: Small numbers of bacteria present in the blood, which may not be multiplying.

    • Viremia: Small numbers of viruses present in the blood, not necessarily replicating.