MLAB 2434 – MICROBIOLOGY KERI BROPHY-MARTINEZ

1. MLAB 2434 – MICROBIOLOGYKERI 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

9. Host Pathogen Interaction

10. Host Pathogen Interaction

11. Host Pathogen Interaction

12. Host Pathogen Interaction

13. Host Pathogen Interaction

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-Pathogen Interaction (cont’d) • Host Resistance Factors: Third Line of Defense • Adaptive/specific immunity

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. • http://garrisonfive.blogspot.com/2009/05/home-sweet-home.html • http://www.5thguy.com/billboards.htm • http://www.thefreedictionary.com/vagrant • Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.