Pathogenesis II host defense of microbes
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The document discusses the pathogenesis, host defense, and pathogenicity of microbes, highlighting the roles of normal flora and various immune responses. It details mechanisms of bacterial infections, including transmission routes, stages of pathogenesis, and the interplay between innate and acquired immunity. Normal flora serve protective functions but may cause disease under certain conditions, especially in immunocompromised individuals.
Pathogenesis II host defense of microbes
- 1. PATHOGENESIS II: HOST DEFENSE AND PAHOGENICITY OF THE MICROBES Dr. Tarek Mahbub Khan MBBS, M.Phil (virology) Assistant professor
- 2. TLO • Outline of host defense against infectious disease • Define normal flora • Distribution of normal flora • Protective function and clinical significance of normal flora • Stages of bacterial pathogenesis • Mode of transmission • Routes of transmission
- 3. MECHANISM OF HOST DEFENSE INNATE AQUIRED Physical barrier Skin Mucus membrane Phagocytic cells Macrophage, PMN Soluble molecules Complements Lysozyme Antibody T lymphocytes
- 4. PHYSICAL BARRIER • SKIN – Keratin layer – Fatty acid from sebaceous gland – Low PH – Normal flora • RESPIRATORY TRACT – Mucus lining, IgA, Ciliary apparatus, alveolar macrophage • GASTROINTESTINAL TRACT – Low stomach PH , enzymes, macrophage in small intestine • VAGINA – Low PH by lactobacilli
- 5. FACTORS THAT CONTRIBUTES TO BACERIAL INFECTION BY BARRIER DAMAGE FACTORS DAMAGE BACTERIAL INFECTION Intravenous catheter Skin Staphylococcus epidermidis, Staphylococcus aureus Diabetes Skin Staphylococcus aureus Burns Skin Pseudomonas aeruginosa Dental extraction Oropharynx Streptococcus viridans
- 6. HOST DEFENSE • INFLAMMATION • PHAGOCYTOSIS
- 7. INFLAMMATORY RESPONSE • PYOGENIC RESPONSE (Result in formation of pus) – Pathogens are pyogenic – Extracellular – Mediated by complements, PMN, antibody – Usually acute • GRANULOMATOUS RESPONSE (Formation of granuloma) – Pathogens are intracellular – Macrophage and helper T cells are the components – Usually chronic
- 9. INFLAMMATORY RESPONSE AGAINST BACTERIAL INFECTION
- 10. EARLY HOST DEFENSE AGAINST BACTERIAL INFECTION
- 11. PHAGOCYTOSIS
- 12. PROCESS OF PHAGOCYTOSIS • MIGRATION – Mediated by IL-8, C5a, Killikrein – Adhesion is mediated by interactions between PMN cells with selectin protein of endothelium and integrin of PMN cells with ICAM • INGESTION – Formation of phagosome – Mediated by IgG, C3b (opsonization) • KILLING
- 13. NORMAL FLORA: role in host defense Normal flora is the term used to describe the various bacteria and fungi that are permanent residents of certain body sites, especially the skin, oropharynx, colon, and vagina
- 14. COMMENSALS Commensals are organisms that derive benefit from another host but do not damage that host. The normal flora are often referred as commensals.
- 15. SIGNIFICANCE OF THE NORMAL FLORA • May produce disease in the following conditions: – In immunocompromised patient – When organisms travel to an unusual site • Colonization resistance: – Occupy receptors of other pathogenic bacteria and thereby limits infection • Some has metabolic function: – Synthesis of vitamin B12 and vitamin K
- 16. NORMAL FLORA OF DIFFERENT BODY SITES • SKIN – Staphylococcus epidermidis, propionibacterium acnes, Candida albicans • RESPIRATORY TRACT – NOSE: Staphylococcus aureus – THROAT: Viridans streptococci, Neisseria species – MOUTH: Eikenella corodens, Bacteroides
- 17. • INTESTINAL TRACT – The small intestine usually contains small numbers of streptococci, lactobacilli, and yeasts, particularly C. albicans. – Escherichia coli • GENITOURINARY TRACT – Group B Streptococci – Candida Albicans NORMAL FLORA OF DIFFERENT BODY SITES
- 18. TYPES OF BACTERIAL INFECTIONS • TWO major mechanisms: – Toxin mediated • Exotoxin • Endotoxin – Invasion and inflammation
- 19. STAGES OF BACTERIAL PATHOGENESIS 1. Transmission into the portal of entry. 2. Evasion of primary host defence 3. Adherence 4. Colonization
- 20. 5. Disease :by toxin production or invasion 6. Host responses 7. Progression or resolution of infection STAGES OF BACTERIAL PATHOGENESIS
- 22. SUMMARY • Host defense is mediated through innate and acquired arm of the immune system • Intracellular pathogens are controlled by macrophage and T cells mediated response • Extracellular pathogens are controlled by complement activation, antibody • Infection may be pyogenic or granulomatous in type • Bacterial disease may be toxin mediated or invasive
- 23. • Normal flora are the permanent resident of certain body sites • They have protective function but some time may produce disease when patient becomes immunocompromised • Transmission may occurs through respiratory, gastrointestinal, skin or genitourinary routes • Vertical transmission occurs from mother to the offspring through placental route, vaginal route or breast milk SUMMARY
- 24. REFERENCE • Warren Levinson. Review of Medical Microbiology and Immunology, 11th edition (2010). Appleton and Lange. • Geo. F. Brooks, Karen C. Carroll, Janet S. Butel, Stephen A. Morse, Timothy A. Mietzner. Medical Microbiology, 25th edition (2010). Appleton & Lange.