QC

Concise Summary of Microbe-Human Interactions

  • Microbe-Human Interactions

    • The human body hosts trillions of microbes (bacteria, fungi, viruses, protozoa).
    • Microbes form the human microbiome, creating a holobiont that affects health and disease.
    • Microbes can be mutualistic, commensal, or pathogenic, with the latter impacting health under certain conditions.

  • Human Microbiome Project (HMP)

    • Demonstrated humans have ~21,000 genes, compared to 8-20 million in microbes.
    • Microbes occupy previously thought sterile areas (lungs, placenta, bloodstream).
    • Composition of microbiome influences health, including susceptibility to infections and treatment effectiveness.

  • Infection Types

    • Disease: Pathological state due to infection (e.g., tuberculosis).
    • Infection: Pathogenic microbes invading host tissues (e.g., Streptococcus pneumoniae causing pneumonia).
    • Colonization: Non-disease-causing presence of microbes (e.g., Lactobacillus in the gut).

  • Pathogen Types

    • True Pathogens: Cause disease in healthy individuals.
    • Opportunistic Pathogens: Cause disease when host defenses weaken.

  • Factors Weakened Host Defenses

    • Age, genetic defects, underlying diseases, stress, chemotherapy.

  • Microbial Antagonism

    • Normal biota prevents overgrowth of harmful microbes and influences immunity.

  • Virulence

    • Ability of a microbe to cause disease; influenced by infectious dose (lower ID typically means higher virulence).

  • Infection Steps

    • Portal of entry, attaching to host tissues, surviving defenses, causing damage, exiting the host.

  • Attachments and Invasion

    • Adhesins, biofilms support adherence to host cells; intracellular pathogens evade immune responses.

  • Host Defenses vs. Pathogen Strategies

    • Phagocytes destroy pathogens; some pathogens evade these defenses through mechanisms like capsules.

  • Host Damage Mechanisms

    • Direct damage from enzymes, toxins (exotoxins and endotoxins), and accidental collateral damage from immune responses.

  • Pathogen Exits

    • Coughing, sneezing, fecal matter, skin shedding, or blood can transmit pathogens.

  • Patterns of Infection

    • Localized, systemic, focal, and mixed infections.

  • Signs & Symptoms

    • Signs: Observable evidence (e.g., fever); Symptoms: Patient-reported experiences (e.g., pain).

  • Transmission

    • Horizontal, vertical, and indirect routes of transmission (via contaminated objects).

  • Viral and Zoonotic Infections

    • Biological vectors carry pathogens; zoonotic diseases transmit from animals to humans.

  • Reservoirs and Carriers

    • Living (humans, animals) and non-living reservoirs (soil, water).
    • Carriers can be asymptomatic but transmit pathogens.

  • Course of Infection

    • Stages: Incubation, prodromal, acute, convalescent; potential latency and sequelae effects.

  • Conclusion

    • Understanding the microbiome, pathogen behavior, infection patterns, and immune responses is crucial for managing health and disease.