This presentation contains slides describing normal microbial flora of human body, significance of normal flora, distribution of normal flora, immune response to infection, source and transmission of infective agents, stages of infection

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

8. ROLEOFCOMPLEMENTSIN
INFECTION

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.