HOST PARASITE RELATIONSHIP

1. HOST PARASITE RELATIONSHIP

2. Introduction of a flora

3. Range of relationships • Saprophytes – Free living microbes subsisting on dead or decaying organic matter. • Parasites – Microbes establishing and multiplying themselves in hosts. • Commensals – Microbes living in complete harmony with host without causing any harm to them. • Pathogens - Microbes capable of causing disease in host.

4. Definitions • Microbial pathogenesis—process of causing disease • Colonization—presence of microbes at site of body • Does not imply tissue damage or disease symptoms • Does imply invasion of site and multiplication

5. Characteristics of Parasitism • Encounter: agent meets host • Entry: agent enters host • Spread: agent spreads • Multiplication: agent multiplies • Damage: agent, host response, or both • Outcome: agent or host wins, or coexist

6. Encounter • In utero • Do not normally come in contact with organisms • Protection of fetal membranes • Do not normally come in contact with organisms from mother • Normally only present sporadically • Exceptions: sexual diseases, virus causes, rubella

7. Encounter • At moment of birth • Comes in contact with organisms present in vaginal canal and on skin • Previously, antibodies passed from mother to fetus • Defenses are good for a period of time, then they wane

8. Encounter • Challenge between man and microbe wages many times during lifetime • Most disappear rapidly • Some become part of normal flora • Only a few cause disease

9. Penetration into Deeper Tissues • Very few organisms can penetrate unbroken skin (worms are an exception) • Some organisms can penetrate epithelial tissue; for example: • S. pneumoniae, Treponemapallidum • Normally after some injury to tissue (many times caused by a virus) • Viruses, by receptors

10. Carried in by Macrophage • Alveolar macrophage trap organisms in lung • Normally carry upward on ciliary epithelium • Some cases, can carry deeper into tissues • Some organisms can live, grow in macrophage: • Legionella • Bordetellapertussis • HIV (via virus-laden macrophage from semen)

11. Primary Infection Reinfection Secondary Infection Focal Infection (Focal Sepsis) Generalized Infection Cross Infection Iatrogenic Infection Endogenous Infection Exogenous Infection Inapparent Infection (Subclinical Infection) Clinical Infection Typical Infection Atypical Infection Latent Infection Compromised host Terms used

12. Human Beings Patients Carriers Healthy Convalescent Temporary Chronic Contact Paradoxical Animals Zoonosis Reservoir Insects Mechanical Biological Soil & Water Food SOURCES OF INFECTION

13. Endemic Epidemic Pandemic Prosodemic Bacteremia Common occurrence while brushing, chewing etc Septicemia Circulation, multiplication, formation of toxins with high swinging fever Pyemia– Septicemia by pyogenic organisms. Produces multiple abscesses in internal organs. Other terms commonly used

14. METHODS OF TRANSMISSION OF INFECTION • Contact • Congenital • Inhalation • Ingestion • Inoculation • Insects • Iatrogenic • Lab Acquired

17. Terms used Pathogenicity (Refers to a species) Virulence (Refers to an isolate) Exaltation Attenuation Factors Adhesion Adhesins Pili Invasiveness Toxigenicity Exotoxins Endotoxins Plasmids Enzyme production-IgA proteases Bacteriophages Communicability Bacterial appandages Infecting dose MID ID50 MLD LD50 Route of Infection Factors predisposing to Microbial Pathogenicity

18. 1. Portal of entry Respiratory Tract - most common portal Gastrointestinal - via food, water contaminated fingers Fungi live on skin Parenteral Route via bites, injections, wounds Multiple portals of entry Tuberculosis - respiratory droplets, food & milk, wounds

19. 2. Dose High virulence fewer organisms needed Lower virulence many organisms needed LD 50 & ID50

20. 3. Tissue penetration Genetic basis E. coli O157:H7 uses unique sites Invasiveness causes structural damage Cell penetration some pathogens live inside the cells

21. 4. Adherence Adhesins (ligands) adhere to receptors Ligands associated with fimbria Mannose is the most common receptor Pili attachment - N. gonorrhoeae attach to cervix and urethra M Proteins - S. pyogenesadhere to throat epithelial cells

22. 6. Enzymes Coagulase Staphylococci Forms fibrin clot Streptokinase Streptococci Dissolves fibrin clot HyaluronidasePneumococci Digests Hyaluronic Staphylococci Acid Streptococci Leukocidin Staphylococci Disintegrates phagocytes Hemolysin Staphylococci Dissolves red blood cells

23. 7. Capsules Reduce phagocytosis Slow drug penetration 8. Plasmid – Extra chromosomal genetic material Antibiotic resistance 9. LysogenicBacteriophage – Imparts additional genetic character eg Diphtheria bacilli acquire ability to produce exotoxin.

24. Protein Heat Labile Secreted by cells. Diffuse out Separable by filtration Enzymatic action Specific effect Specific tissue affinity Active in small qty Highly antigenic Action neutralized by specific antibody Can be toxoided Mainly produced by Gram + bacteria. Few Gram – ve bact Protein-Polysaccharide-Lipid Complex Heat Stable Part of cell wall. No diffusion Obtained only by cell lysis No Enzymatic action Effect non-specific Non-specific Active in large doses Weakly antigenic Antibody does not neutralize Can not be toxoided Produced only by Gram negative bacteria Exo Vs Endotoxins

25. Pyrogenicity Lethal action  Blood Pressure Activation of complement Intravascular coagulation Leucopoenia / Leukocytosis  Glucose / Glycogen synthesis in Liver Stimulation of B cells Macrophage inhibition Interferon release Induction of prostaglandin synthesis Biological activities of the Endotoxins