Antimicrobial Susceptibility Testing (AST) MLAB 2434 – Microbiology Keri Brophy-Martinez.
MLAB 2434 – MICROBIOLOGY KERI BROPHY-MARTINEZ
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Transcript of MLAB 2434 – MICROBIOLOGY KERI BROPHY-MARTINEZ
MLAB 2434 – MICROBIOLOGYKERI 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 floraCarriers?
Host Pathogen Interaction Factors that determine normal
floraAvailability of nutrientsMoisture of anatomical sitePresence of bile, lysozyme, fatty
acidspH
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 DefenseAdaptive/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,
STDsCuts and BitesArthropods ( 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.