Immune System and Infection Transmission Quiz

Bacterial Pathogenesis Mechanisms

• Bacteria cause disease through infection, which involves the growth and multiplication of bacteria within or on the body, potentially leading to disease development.
• Infection does not always result in disease.
• The host's defense mechanisms play a crucial role; infectious disease occurs when the damage caused by pathogens exceeds the host's immune system's response.
• Bacteria can be classified into different categories based on their interaction with the host:
  • Saprophytes: bacteria that grow in soil and live on dead organic matter.
  • Commensal bacteria: harmless microbes that live on the host without causing harm.
  • Pathogenic bacteria: capable of causing disease.
  • Primary pathogens: cause disease in healthy individuals.
  • Opportunistic pathogens: take advantage of preexisting conditions (like weakened immune systems) to cause disease.
• Infection routes include: endogenous (self-infection) and exogenous (cross-infection).
  • Endogenous infection: commensal bacteria in one part of the body moving to another.
  • Exogenous infection: transmission from another source.

Sources of Exogenous Infections

• Patients: transmission from patients suffering from an active disease to healthy individuals.
• Infected animals: zoonotic infections.
• Soil: saprophytic microbes present in soil, vegetation, and similar environments.
• Carriers: individuals harboring pathogens without showing clinical symptoms, hence capable of spreading infections to others; classified as convalescent, chronic, or healthy carriers.

Modes of Transmission

• Ingestion (food or water).
• Inhalation (respiratory tract).
• Trauma.
• Direct contact (skin-to-skin).
• Sexual transmission.
• Blood-borne transmission.
• Vector-borne transmission.
• Vertical transmission (mother-to-child).

Mechanisms of Infection

• Exposure: Initial contact with pathogens.
• Adhesion: Pathogens attach to host cells.
• Invasion: Pathogens enter host cells or tissues.
• Colonization: Pathogens multiply and establish themselves.
• Toxicity: Release of toxins, directly harming host cells or disrupting their functions. -Tissue damage can manifest as disease.

Microbial Toxins

• Microbial products directly harming tissues and altering host metabolism, often causing major symptoms.

  • Exotoxins: Secreted toxins with enzymatic activity. They often cause illness (e.g. diphtheria, tetanus, cholera)

  • Endotoxins: Components of outer cell wall of Gram-negative bacteria. Released upon cell death, stimulating potent inflammatory reactions.

  • Classified by structure and function.

Defense Mechanisms

• Innate (non-specific): Immediate responses (e.g., physical barriers, inflammation, phagocytosis, complement system, interferons).

• Adaptive (specific): Immune response adapted to particular pathogens (e.g., antibodies, T cells).

• Innate responses: immediate responses to infection.

• Innate, antigen-nonspecific defenses: local response, including phagocytes (macrophages, neutrophils), natural killer (NK) cells, dendritic cells, interferons, complement system, inflammation/fever, antimicrobial peptides (AMPs).

• Non-specific physical and chemical defenses: skin, mucous membranes, stomach acids, lysozyme in tears, expulsion (coughing, sneezing, vomiting, diarrhea).

• Adaptive, antigen-specific responses: antibodies and T cells.

Complement System

• The complement system is a crucial part of the innate immune system participating in the destruction of pathogens.
• Various pathways (classical, alternative, lectin) activate the complement cascade leading to the formation of the membrane attack complex (MAC) and a series of other crucial immune responses.

Phagocytes and Inflammation

• Phagocytes (such as macrophages and neutrophils) engulf and destroy pathogens, initiating an inflammatory response.
• Inflammation is a localized response following injury or infection, characterized by redness, swelling, heat, and pain; it's a crucial part of the body´s defenses.

Bacterial Pathogenesis

• Disease results from tissue damage caused by toxins or direct killing.
• Microbes can infect distant tissues.