BACTERIAL VIRULENCE FACTORS

• Virulence factors


  Bacterial traits that confer pathogenicity

  
• Virulence factors


  • Enable processes such as adhesion, biofilm formation, motility, toxin secretion, immune evasion, colonization, and bacterial cell–cell communication
  • Allow bacteria to colonize (extracellular and/or intracellular) niches in hosts and produce disease

  
• Quorum-sensing


  • Bacterial cell-cell communication
  • Virulence gene expression control

  
• Secretion systems


  • Virulence factor delivery
  • Protein secretion and transport
  • DNA uptake and transfer
• LPS


  • Inflammation
  • Tissue damage
• Pili


  • Adhesion
  • DNA uptake
  • DNA transfer
  • Motility
• Efflux pumps


  • Antibiotic secretion
  • Siderophore secretion
  • Other secretion of toxin compounds
• Two component system


  • Virulence factor regulation
• Flagella


  • Motility
  • Host cell adhesion
• Toxin production


  • Tissue damage
  • Invasion
  • Impairs immune response
• Surface-associated proteins


  • Host cell adhesion and colonization
  • Nutrient acquisition
  • Cell invasion and immune evasion
  • Biofilm formation

  
• Virulence factors


  • Toxins
  • Capsule
  • Flagella
  • Fimbriae
  • Quorum sensing
  • Biofilm
  • Transfer of VFs

  
• Exotoxins


  • Secreted by the bacteria
  • Highly antigenic proteins
  • Different types according to mechanisms and targets

  
• Types of exotoxins


  • A-B toxins
  • Type III toxins
  • Superantigens
  • Membrane-damaging toxins

  
• 1. B toxins and Type III toxins


  • They usually modulate the host cell metabolism

  
• Membrane-damaging toxins


  • Pore-forming toxins
  • Lipases
  • Cytotoxic = kills the cell
• Superantigens


  • Trigger excessive stimulation of T lymphocytes
  • Resulting in massive T-cell proliferation and cytokine release
  • Fever, arthritis, dermatitis, shock
• Shock


  • Life-threatening condition that occurs when the body is not getting enough blood flow
  • Lack of blood flow means the cells and organs do not get enough oxygen and nutrients to function properly
  • Many organs can be damaged as a result (organic failure)
• Extracellular matrix (EM) toxins

  • Hyarunidases
  • Streptokinase
  • Collagenases
  • Hyaluronic acids
  • Collagen
  • Toxins allow free-movement of bacteria
• Endotoxin in small amounts can induce symptoms of inflammation, fever, and leukopenia, and damage to blood vessels, finally leading to hypotension
• High endotoxin levels can cause shock (organ failure) and intravascular coagulation
• The intravascular release or presence of LPS present massive effects on the hosts, and their impact is concentration dependent
• Capsule


  • Protection against
  • Significant role in determining access of certain molecules to the cell membrane, mediating adherence to surfaces, and increasing tolerance of desiccation
• Flagella


  • Motility
  • Adhesion
  • Participates in biofilm formation
  • Modulate immune system of eukaryotic cells

  
• Pili/fimbriae


  • Their presence greatly enhances the bacteria's ability to attach to the host and establish infection

  
• Quorum-sensing


  • Bacterial cell-cell communication by small signal molecules (pheromones, autoinducers)
  • Effect on virulence and other metabolic gene expression control
  • When the bacterial population reaches a defined density (a bacterial quorum), the pheromones attain a critical threshold concentration at which they coordinate expression of bacterial genes, so that the colonizing bacteria act as a community rather than as individuals
  • Low density: autoinducers diffuse away from bacteria promoting individual cell behavior
  • High density: autoinducers bind to receptors and promote group behavior

  
• Biofilm formation


  • Clusters of bacteria that are attached to a surface and/or to each other and embedded in a self-produced matrix
  • Consists of substances like proteins, polysaccharide and released DNA
  • Protective organization or arrangement

  
• Transfer of virulence factors (VF)

  1. Transformation: Bacteria acquire free DNA from the environment, some of which may be VF genes

  2. Transduction: Bacteriophages (viruses of bacteria) transfer bacterial DNA from one bacterium to another, some of which may be VF genes

  3. Conjugation: One bacterium can transfer a plasmid (mobile DNA) to another bacterium, usually containing VF genes
• Emergence and dissemination of Antimicrobial drug resistance
• Selection of serious pathogenic strains in the clinics