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

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

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

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

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

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

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

Host Pathogen Interaction

Host Pathogen Interaction

Host Pathogen Interaction

Host Pathogen Interaction

Host Pathogen Interaction

Host Pathogen Interaction

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

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

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.)

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

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

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

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

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

Inflammatory process

Host-Pathogen Interaction (cont’d)

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

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)

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)

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

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.