Virulence Factors PDF

**Virulence Factors** **Leaning outcomes** **1. Explain how virulence factors contribute to signs and symptoms of infectious diseases.** - **Answer:** Virulence factors are molecules produced by pathogens that facilitate infection, tissue damage, and immune evasion. These factors includ...

**Virulence Factors** **Leaning outcomes** **1. Explain how virulence factors contribute to signs and symptoms of infectious diseases.** - **Answer:** Virulence factors are molecules produced by pathogens that facilitate infection, tissue damage, and immune evasion. These factors include adhesins (allow pathogens to attach to host cells), exoenzymes (break down host tissues to promote invasion), and toxins (damage host cells). For example, exotoxins like *cholera toxin* cause diarrhea by disrupting normal cellular function, while endotoxins in Gram-negative bacteria trigger systemic inflammation, leading to fever and shock​(Virulence Factors of Ba...). **2. Differentiate between endotoxins and exotoxins.** - **Answer:** - **Endotoxins:** Found in the outer membrane of Gram-negative bacteria (Lipid A of lipopolysaccharides). They cause general inflammatory responses like fever and can lead to septic shock in high concentrations. They are heat-stable. - **Exotoxins:** Protein toxins secreted mainly by Gram-positive bacteria, but also by some Gram-negatives. They target specific cells and tissues, causing damage through precise mechanisms (e.g., *botulinum toxin*inhibits neurotransmitter release). Exotoxins are heat-labile and highly potent at low doses​(Virulence Factors of Ba...). **3. Describe and differentiate between various types of exotoxins.** - **Answer:** - **Intracellular-targeting toxins (A-B toxins):** These toxins enter cells and disrupt specific cellular functions. Examples include *diphtheria toxin* (inhibits protein synthesis) and *botulinum toxin* (inhibits neurotransmitter release, causing paralysis). - **Membrane-disrupting toxins:** These toxins damage host cell membranes by forming pores or degrading phospholipids, leading to cell lysis. Examples include *streptolysin* from *Streptococcus pyogenes*. - **Superantigens:** These exotoxins cause an excessive immune response by activating a large number of T-cells, resulting in a cytokine storm. An example is *toxic shock syndrome toxin* (TSST) from *Staphylococcus aureus*​(Virulence Factors of Ba...). **4. Describe the mechanisms viruses use for adhesion and antigenic variation.** - **Answer:** - **Adhesion Mechanisms:** Viruses use specific viral proteins (adhesins) to bind to host cell receptors. For example, *Influenza virus* uses hemagglutinin to bind to sialic acid on respiratory epithelial cells, while *HIV*uses glycoprotein gp120 to bind to CD4 and co-receptors CCR5/CXCR4 on immune cells. - **Antigenic Variation:** This mechanism allows viruses to evade the immune system by changing surface proteins. **Antigenic drift** involves small mutations in viral proteins, while **antigenic shift** results from reassortment of viral genes, leading to the emergence of new viral strains (e.g., in *Influenza viruses*)​(Virulence Factors of Ba...).