Microbial_Mechanisms_of_Pathogenicity_Summary.pptx

Bacterial pathogenesis, Viral Pathogenesis, Fungal Pathogenesis

1. Microbial Mechanisms of Pathogenicity Summarized Presentation Based on Tortora, Funke, and Case - Microbiology: An Introduction (13th Edition)

2. Introduction to Pathogenicity • Pathogenicity: the ability of a microorganism to cause disease. • Virulence: degree or intensity of pathogenicity. • Opportunistic pathogens cause disease under special conditions (e.g., weakened host). • Infection occurs when pathogens invade and multiply within the host body.

3. Portals of Entry • Pathogens enter the host through specific routes: – Mucous membranes (respiratory, gastrointestinal, urogenital tracts) – Skin (cuts, bites, injections) – Parenteral route (direct deposition into tissues) • Preferred portal of entry influences the severity of disease.

4. Adherence to Host Cells • Adhesins or ligands on microbial surfaces bind specifically to host cell receptors. • Examples: – Streptococcus mutans: adheres to teeth via glycocalyx. – Neisseria gonorrhoeae: uses fimbriae for attachment. • Biofilms enhance adherence and resistance to immune defenses.

5. Penetration of Host Defenses • Capsules: prevent phagocytosis (e.g., Streptococcus pneumoniae). • Cell wall components: M protein, opa protein, and mycolic acid aid evasion. • Enzymes (e.g., coagulase, kinase, hyaluronidase, collagenase) facilitate tissue invasion. • Antigenic variation helps microbes evade immune recognition.

6. Damage to Host Cells • Pathogens damage host tissues by: – Using host nutrients (e.g., siderophores for iron acquisition) – Direct damage during infection – Production of toxins (exotoxins and endotoxins) • Exotoxins: proteins secreted by bacteria, highly specific effects. • Endotoxins: lipopolysaccharides from Gram-negative bacteria cause fever and shock.

7. Exotoxins vs Endotoxins • Exotoxins: – Secreted proteins from Gram-positive and Gram-negative bacteria. – Highly potent, antigenic, and heat-labile. • Endotoxins: – Part of outer membrane of Gram-negative bacteria (lipid A of LPS). – Released during cell death or division. – Cause systemic effects like fever, inflammation, and shock.

8. Pathogenic Properties of Viruses • Viruses cause cytopathic effects (CPE) such as: – Inclusion bodies, cell fusion (syncytia formation), chromosomal damage. – Interferon production and apoptosis induction. • Latent infections (e.g., herpesvirus) and oncogenic viruses (e.g., HPV) alter host cell behavior.

9. Eukaryotic Pathogen Mechanisms • Fungi: produce mycotoxins and proteases that damage host tissues. • Protozoa: invade and destroy host cells; undergo antigenic variation. • Helminths: cause damage by metabolic waste and tissue migration.

10. Summary • Pathogenicity depends on microbial virulence factors and host susceptibility. • Mechanisms include entry, adherence, evasion, and toxin production. • Understanding these mechanisms helps in disease prevention and treatment.