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, Treponema pallidum
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
Bordetella pertussis
HIV (via virus-laden macrophage from semen)

11. Terms used 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

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

13. Other terms commonly used
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.

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

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

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 18

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

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 20

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. pyogenes adhere to throat epithelial cells

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

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

24. Exo Vs Endotoxins Protein-Polysaccharide-Lipid Complex Protein
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
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

25. Biological activities of the Endotoxins
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