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2013-08-29 22:50:57

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  1. Describe the complex interplay between host and parasite
    Understanding why it is that most host-microbe contacts DO NOT result in disease, and what changes to make disease arise.
  2. What percentage of worldwide deaths are attributed to infectious diseases?
    • More than 20%
    • Infectious diseases are a major problem in the resource-poor world
    • Economic costs are enormous
  3. What are the top six infectious diseases in the world
    • 1. Acute respiratory infections ~6.8 million
    • 2. HIV/AIDS (1 agent) ~3.2 million
    • 3. Diarrheal diseases ~3.1 million
    • 4. TB (1 agent) ~1.8 million
    • 5. Malaria ~1.2 million
    • 6. Measles ~1.2 million
  4. Describe emergence/reemergence of infections
    • Re-emerging: TB, malaria, hepatits, cholera, dengue fever
    • Emerging: 25+ since 1980
    • HIV is most important
  5. What are the two groups of microbes? What do they contain?
    • Non-cellular microbes
    • viruses and viroids: have genetic material but lack cell membranes, cytoplasm, and the machinery for synthesizing macrmolecules
    • Prions: proteinaceous infectious particles that cause diseass such as Creutzfeldt-Jakob disease, and kuru
    • Cellular microbes
    • prokaryotes: Bacteria and Archaea
    • eukaryotes: Eukarya
  6. What is the difference between viruses and viroids?
    • Viruses have a capsid surrounding them
    • Viroids are "naked" RNA that is only found to infect plants
  7. Microparasites vs macroparasites
    • Microparasites: viruses, bacteria, protozoa and fungi
    • Often complete a full life cycle within one host
    • Can multiply to produce a very large number of progeny (overwhelming infection)
    • Macroparasites: worms, arthropods
    • Often grow in one host and reproduce outside that host
  8. What is the basis of all host-pathogen relationships?
    • Exploitation by the pathogen of the host to obtain metabolic materials
    • Nutrients (cellular pathogens)
    • Synthetic machinery (viral pathogens)
  9. What are the three potential host-pathogen relationships?
    • Extracellular pathogens: live either within tissues or on the surface of the body cavities (between cells).
    • Macroparasites are almost always extracellular
    • Obligate intracellular pathogens: must invade host cells to replicate.
    • Viruses, Chlamydia, Rickettsia
    • Facultative intracellular pathogens: can replicate either in or out of cell
    • Mycobacteria
  10. Intracellular pathogen's advantages
    • Access to host's nutrient supply
    • Access to host's genetic machinery
    • Escape from host's defense mechanisms and antimicrobial defenses
  11. Problems caused by intracellular pathogen
    • Intracellular killing mechanisms may destroy the host cell (tissue damage)
    • It is difficult for drugs or antibiotics to achieve selective action against the pathogen while leaving the host cell intact (mitochondria may be targeted)
    • Many intracellular pathogens live inside cells responsible for immune response, depressing their defensive capabilities
  12. Extracellular pathogen's advantages
    Can grow, reproduce freely, and move extensively within the tissues of the body
  13. Problems caused by extracellular pathogen
    • Spread rapidly through extracellular fluids or move rapidly over surface resulting in a widespread infection quickly
    • Require different defense mechanisms than intracellular parasites
  14. Host defense mechanisms for extracellular pathogens
    • Antibodies are primary defense, and they function in 3 major ways
    • 1. neutralization: binding can block the association of the pathogen with its target
    • 2. opsonization: binding can facilitate its uptake/destruction by phagocytes
    • 3. complement activation: binding can activate a complement cascade resulting in lysis of bacterial cells
  15. Host defense mechanisms for intracellular pathogens
    • Cell-mediated responses are the primary defense, which vary based on location of pathogen
    • Viruses and bacteria in the cytoplasm: Tcyto recognizes and induces apoptosis in infected cells
    • Bacteria and parasites within endosomes: TH1 recognizes and activates infected cells to destroy the pathogen inside
  16. Describe the classification of bacteria
    • Shape: cocci, spiral, bacilli
    • Gram reaction: +/-
    • Gram+ has thick peptidoglycan layer
    • Gram- has thin peptidoglycan layer with outer membrane
    • Atmosphere: obligate anaerobe, microaerophile, obligate anaerobe, facultative anaerobe, capnophile (increased CO2 levels)
    • Spores: presence, shape, and position within bacterial cell
    • Biochemistry: oxidase, catalase, lactase, etc
    • Serolgy: interaction with antibodies
    • Genetics: DNA sequences of key genes
  17. Summary of medically important groups of bacteria and their "star players" <very important>
    • Staphylococci (catalase+):
    • S. aureus (yellow colonies)
    • Steptococci (catalase-):
    • S. pyogenese (sore throat/rheumatic fever)
    • S. agalactiae (neonatal meningitis and pneumonia)
    • N. meningitides (meningitis)
    • N. gonorrhoeae (urethritis, gonorrhea)
    • Haemophilus and Bordetella (respiratory pathogens)
    • Brucella and Pasteurella (zoonotic agents)
    • Sporing aerobic:
    • Bacillus
    • Sporing anaerobic:
    • Clostridium
    • Non-sporing:
    • Listeria monocytogens andCorynebacterium
    • Salmonella (diarrhea)
    • Shigella (bloody diarrhea)
    • Yersinia (deadly)
    • Escherichia, Proteus, Pseudomonas, Burkholderia, and Legionella
    • Helicobacter (stomach cancer)
    • Campylobacter (food born acute diarrhea)
    • Treponema (syphyllus)
    • Borrelia and Leptospira
    • MYCOPLASMA AND CHLAMYDIA: common respiratory and sexually transmitted infections
    • RICKETTSIA: agents for typhus are rarer severe infections
  18. Describe the bacterial structures important for classification and pathogenicity in detail
    • A polysaccharide layer external to the cell wall
    • Hard = capsule, soft = slime layer (biofilm)
    • Most important virulence factor
    • Protect from phagocytosis and antibiotics
    • Only capsulated S. pneumonia can cause a fatal infection
    • A surface antigen that can strongly stimulate inflammation
    • Endotoxin found only in gram negative bacteria
    • Protects from complement-mediated lysis
    • Causes septic shock (systemic blood vessel expansion/blood pressure drop)
    • More rigid than flagella
    • Function in attachment to other bacteria (sex pili) or host cells (common pili)
    • Adherence to host involves specific interactions (eg. E. coli is normal flora in gut, but causes UTI in urethra)
    • May prevent phagocytosis
    • Allow for movement
    • Polar monotrichous: single flagellum on one side
    • Polar lophotrichous: multiple flagella on one side
    • Amphitrichous: flagella/um on both sides
    • Peritrichous: flagella all over
    • Flagellins (the monomer) are STRONGLY antigenic
    • H antigens (flagellar) are important targets of antibody response
    • SPORES
    • highy resistant endospores in response to adverse conditions
    • Allow extended survival (dormant for millions of years)
    • Clostridium and Bacillus spores are responsible for tetanus and anthrax