Bacterial Virulence Factors

Virulence Factors

• Definition: Traits that enable bacteria to exhibit pathogenicity.

• Functions:

  • Facilitate adhesion

  • Promote biofilm formation

  • Enable motility

  • Support toxin secretion

  • Assist in immune evasion

  • Aid in colonization of host niches

• Importance: Critical for bacteria to establish infection and cause disease.

Types of Virulence Factors

Quorum Sensing

• Description: Mechanism of bacterial cell-cell communication.

• Function: Regulates virulence gene expression based on population density.

Secretion Systems

• Roles: Delivery of virulence factors, protein secretion, and DNA intake.

Surface-Associated Proteins

• Functions:

  • Adhesion to host cells

  • Nutrient acquisition

  • Immune evasion

  • Biofilm formation

LPS (Lipopolysaccharide)

• Role in Pathogenesis: Causes inflammation and tissue damage.

Pili (Fimbriae)

• Functions:

  • Facilitation of adhesion

  • DNA uptake and transfer

  • Motility enhancement.

Efflux Pumps

• Functions:

  • Antibiotic secretion

  • Siderophore secretion (iron acquisition)

  • Secretion of toxic compounds.

Flagella

• Roles:

  • Motility

  • Adhesion to host cells.

Toxin Production

• Impact: Causes tissue damage, invasion, and impairment of immune responses.

Example of Bacterial Pathogen: Bartonella

• Infection Pathway:

  • Entry via dermis and vasculature.

  • Bacterial manipulation of host cells during infection.

  • Utilizes proteins such as InlB and InlA for cellular entry.

  • Effects on host defenses: Actin rearrangement, lysosome permeabilization, and modulation of immune responses.

Overview of Bacterial Toxins

Types of Toxins

• Exotoxins: Secreted proteins that can be highly antigenic.

  • Types include:

    • A-B toxins

    • Type III toxins

    • Superantigens

    • Membrane-damaging toxins.

• Endotoxins: Found in the outer membranes of Gram-negative bacteria (LPS).

  • Causes immune responses like inflammation and fever.

Exotoxins: Mechanisms of Action

• A-B Toxins: Modulate host cell metabolism.

• Membrane-Damaging Toxins: Can lead to cytolysis.

• Superantigens: Trigger excessive T-cell stimulation, leading to conditions like shock and fever.

Impact and Consequences of Toxins

• Shock: Life-threatening condition due to inadequate blood flow resulting in organ failure.

Extracellular Matrix (EM) Toxins

• Examples include: Hyaluronidases, Streptokinase, Collagenases.

• Function: Facilitate bacterial movement through tissues.

Virulence Factor Transfer Mechanisms

• Transformation: Uptake of free DNA, possibly including VF genes.

• Transduction: Bacteriophage-mediated transfer of bacterial DNA.

• Conjugation: Transfer of plasmids containing VF genes between bacteria.

Consequences of VF Transfer

• Emergence of Antimicrobial Resistance: Promotes the development of serious pathogenic strains.