Bacterial Virulence Factors Overview

Bacterial Virulence Factors

• Adhesion: bacteria use fimbriae, pili, capsules, and other surface proteins to attach to host cells.
• Invasion : bacteria use enzymes to break down host tissues and evade immune defenses. Examples of enzymes: hyaluronidase, collagenase, and coagulase.
• Toxins: bacteria produce toxins, these can act locally or systemically and damage host cells.
  • Exotoxins: are secreted outside bacterial cell walls, targeting specific cells or tissues.
    • A-B toxins: have two parts, an A subunit that has an enzymatic effect and a B subunit that binds to a host cell receptor.
    • Superantigens: stimulate excessive immune response, causing cytokine release.
  • Endotoxins: are located in the outer membrane of Gram-negative bacteria, released when bacteria die or lyse.
• Biofilms: bacteria can form biofilms, these are communities of bacteria enclosed in a slime layer, making them less susceptible to antibiotics and immune responses.

Viral Virulence Factors

• Attachment: viruses use specific receptors on host cells for attachment, they bind to these receptors, called ligands
• Entry: viruses use different mechanisms to enter host cells, including endocytosis and fusion
• Replication: viruses replicate inside host cells, some hijack cellular machinery, others bring their own replication enzymes
• Assembly and Release: newly synthesized viral components assemble into new viral particles, and the host cell may lyse or release virus particles through budding
• Evasion of Immune Response: viruses can evade the host immune response by altering their antigens, inhibiting interferon production, or developing resistance to antiviral drugs.

Virulence Factors in Disease

• Factors contribute to disease progression: disease progression relies upon the interplay between the pathogen's virulence factors and the host's immune system.
• Dissemination: Spread of pathogens within the host can be caused by specific virulence factors, this can lead to systemic infections.

Genetic Shift and Drift

• Antigenic Shift: a significant change in the genetic makeup of a virus, caused by the reassortment of viral genes (typically influenza viruses).
• Antigenic Drift: gradual viral mutations leading to changes in antigens, making it harder for immune systems to recognize and fight the virus (also typically influenza viruses).