Lecture Notes: Pathogenicity and Virulence Factors

Key Definitions

• Pathogenicity: The ability of a microorganism to cause disease.
• Virulence: The intensity or severity of the disease caused by a microorganism.

Virulence Factors

• Structural or physiological features that enable a microorganism to cause disease.
• Must allow the microorganism to survive host defenses to be considered virulence factors.

Examples of Virulence Factors

• Adhesion Pili: Structures that allow microorganisms to stick to host cells, making them more dangerous.
• Enzymes and Toxins: Substances that disrupt host homeostasis.

Modes of Entry for Bacteria

• Skin: Breaks in the skin allow direct entry.
• Mucus Membranes: Line orifices; a common entry point.
• Sexual Transmission: Direct contact transmission.
• Inhalation: Airborne transmission.
• Fomites: Non-living objects like door handles and phones.

Specific Virulence Factors

Adhesion and Colonization

• Adhesin Proteins: Found on pili, allow bacteria to stick to host cells.
• Capsules: Thick protective layers making bacteria harder to kill and allowing adherence.
• Phagocytosis Blocking: Adhesins can prevent immune cells from engulfing bacteria.

Enzymes

• Hyaluronidase: Enzyme that breaks down hyaluronic acid, known as "spreading factor".
• Catalase: Breaks down hydrogen peroxide to avoid oxidative damage.
• Coagulase: Converts fibrinogen to fibrin, forming clots for bacteria to hide in.
• Streptokinase: Dissolves clots, allowing bacteria to spread.

Toxins

• Exotoxins: Strong, soluble toxins secreted by mostly gram-positive bacteria.
  • Hemolysins: Break open red blood cells.
  • Leukocidins: Destroy white blood cells.
• Endotoxins: Weak toxins released in large quantities, associated with gram-negative bacteria.
  • Lipopolysaccharide: Released by gram-negative bacteria, can cause endotoxic shock.

Hemolysis and Identification

• Alpha Hemolysis: Partial breakdown of hemoglobin (greenish hue on blood agar).
• Beta Hemolysis: Complete breakdown of hemoglobin (clear, translucent area on blood agar).
• Gamma Hemolysis: No hemolysis, no destruction of red blood cells.

Visual Aids

• Images demonstrate various factors such as physical structures (e.g., adhesion pili) and effects like hemolysis.

Lab Applications

• Recognizing types of hemolysis on blood agar plates helps in identifying bacterial species, particularly streptococci.

These notes highlight the primary aspects discussed in the lecture regarding virulence factors and their role in pathogenicity. Understanding these elements is crucial for identifying and combating infectious agents.