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MLAB 2434 – MICROBIOLOGY KERI BROPHY-MARTINEZ Host-Pathogen Interaction.

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Presentation on theme: "MLAB 2434 – MICROBIOLOGY KERI BROPHY-MARTINEZ Host-Pathogen Interaction."— Presentation transcript:

1 MLAB 2434 – MICROBIOLOGY KERI BROPHY-MARTINEZ Host-Pathogen Interaction

2 Host Pathogen Interaction Origin of Microbial Flora Symbiosis: association of 2 organisms living together Commensalism: organism benefit with no benefit or harm to the host Parasitism: microbe gains at host expense

3 Host-Pathogen Interaction (cont’d) Terms Pathogen – microbe that can cause disease in a susceptible host Opportunistic Pathogen – microbe that can cause disease only if a significant change occurs in host resistance or within the organism itself Opportunistic infections- infections caused by opportunistic pathogens

4 Host-Pathogen Interaction (cont’d) Terms Iatrogenic Infections – resulting from medical treatment or procedures Hospital-acquired Infections- acquired in the hospital or another health care setting

5 Host Pathogen Interaction Characteristics of Normal Flora Resident flora vs. transient flora Carriers?

6 Host Pathogen Interaction Factors that determine normal flora Availability of nutrients Moisture of anatomical site Presence of bile, lysozyme, fatty acids pH

7 Host Pathogen Interaction Colonization Persistent survival of a microbe on a surface of the human body. Dictated by the defenses of the body Dictated by the microbes ability to survive

8 Host Pathogen Interaction

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14 Host-Pathogen Interaction (cont’d) Virulence – relative ability of a microorganism to cause disease, or the degree of pathogenicity

15 Host-Pathogen Interaction (cont’d) Infectious Agent Steps Adherence – most infectious agents must attach to host cells before infection occurs Proliferation – pathogens must be able to replicate after attachment to host cells (overcome host resistance factors) Tissue Damage – makes the infection visible; results from toxins or from host inflammatory substances

16 Host-Pathogen Interaction (cont’d) Invasion – all pathogens have the ability to penetrate and grow in tissues Dissemination Spread of organisms to distant sites Some pathogens stay at site (C. diphtheriae); others spread (Salmonella ssp.)

17 Host-Pathogen Interaction (cont’d) Virulence factors – factors such as capsules, toxins, enzymes, cell wall receptors, pili, etc. that allow pathogens to evade or overcome host defenses & enable them to cause disease

18 Host-Pathogen Interaction (cont’d) Virulence factors Attachment Fimbriae/pili Resist phagocytosis Capsules Protein A Leukocidins Ability to Move Flagella

19 Host-Pathogen Interaction (cont’d) Virulence factors (con’t) IgA protease Toxin production Endotoxin Exotoxin Exoenzyme production Necrotizing enzymes Coagulase Kinases Hyaluronidase Hemolysins

20 Host-Pathogen Interaction (cont’d) Host Resistance Factors: First Line of Defense Physical barriers – skin, mucous membranes Cleansing mechanisms Desquamation (shedding of skin) Fluids of the eye (IgA and lysozyme) Respiratory, digestive, urinary, and genital tracts have fluids(mucous) and movements( cilia/ peristalsis) to cleanse the surfaces

21 Host-Pathogen Interaction (cont’d) Host Resistance Factors: Second Line of Defense Inflammatory response Vasodilation Increased permeability of capillaries Arrival of leukocytes Chemotaxis Phagocytosis Immune Responses: innate

22 Inflammatory process

23 Host-Pathogen Interaction (cont’d)

24 Host Resistance Factors: Third Line of Defense Adaptive/specific immunity

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26 Host-Pathogen Interaction (cont’d) Routes of Transmission Airborne Coughing, sneezing, talking Droplet nuclei Airborne pathogens must be resistant to drying and inactivation by ultraviolet light Examples: Strep throat, otitis media, diphtheria, rhinoviruses (colds)

27 Host-Pathogen Interaction (cont’d) Transmission by Food and Water Ingestion of contaminated food or water Sometimes oral-fecal route Pathogens must be able to survive stomach conditions and compete with normal flora of the gut Pre-formed toxins (Clostridium botulinum, S. aureus) vs. toxins produced after infection (C. difficile, V. cholerae)

28 Host-Pathogen Interaction (cont’d) Close Contact Passage of organisms by salivary, skin, and genital contact Examples: Infectious mononucleosis, STDs Cuts and Bites Arthropods ( ticks, fleas) Zoonoses – diseases of animals accidentally transmitted to humans; examples: plague, rabies, tularemia

29 References Engelkirk, P., & Duben-Engelkirk, J. (2008). Laboratory Diagnosis of Infectious Diseases: Essentials of Diagnostic Microbiology. Baltimore, MD: Lippincott Williams and Wilkins. home.html Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.


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