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2013-10-03 13:32:14

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  1. What are the obligatory steps for infection and their corresponding phenomenon in the body
    • Attachment and/or entry into body (infection)
    • Local or general spread in the body (spread)
    • Multiplication (multiplication)
    • Evasion of host defenses (evasion of host defenses)
    • Shedding from the body or exit (transmission)
    • Causing damage in the host (pathology, disease)
    • *not necessary, but can be essential for shedding
  2. What are the four types of infection with specific examples
    • 1. Microbes with specific mechanisms for attaching to, or penetrating, the body surfaces of normal healthy hosts
    • eg. most viruses, and certain bacteria
    • 2. Microbes introduced into normal healthy hosts by biting arthropods
    • eg. malaria, plague, typhus, yellow fever
    • 3. Microbes introduced into normal healthy hosts via skin wounds or animal bites
    • eg. clostridia, rabies, Pasteurella multocida (avian cholera)
    • Microbes able to infect a host only when surface or systemic defenses are impaired
  3. What variables affect the disease expression in an individual?  Example of infections which give a fairly consistent disease expression.  Example of infections that do not.
    • Infecting dose and route
    • age
    • sex
    • presence of other microbes
    • nutritional status
    • genetic background
    • consistent: measles, cholera
    • wide spectrum: syphilis
  4. List the body surfaces that can be sites of microbial infection
    • Skin
    • Respiratory tract
    • Gastrointestinal tract
    • Urogenital tract
    • Oropharynx
  5. What tends to inactivate non normal-flora microbes on the skin?
    • Fatty acids (pH ~5.5)
    • antimicrobial secretions by sebaceous and other glands
    • certain peptides formed by keratinocytes
    • materials produced by the normal skin flora
  6. Give examples of microbes that can traverse unbroken skin to cause infection
    • leptospira
    • larvae of Ancylostoma
    • larvae of Schistosoma
  7. What is the world's most common zoonosis?  Describe the typical infection route
    Leptospirosis: commonly transmitted by animal-urine infected water that contacts skin, eyes, or mucous membranes
  8. What are the two methods of infectious agent transmission by biting arthropods w/ description AND example
    • Mechanical transmission: pathogen on insect feet or other body part
    • eg houseflies can transfer typhoid fever and bacillary dystentery (shigellosis) from infected feces to food
    • Biological transmission: active transmission between hosts
    • eg. arthropod bites infected person, pathogen reproduces inside vector w/o harming the vector, and is transmitted to a new host during a blood feed
  9. What helps to prevent the conjunctiva from infection? What can compromise it?
    • Continuous flushing action of tears
    • Tears include lysozyme and other microbial peptides
    • Physical "windshield wiper" action of eyelid
    • Compromised by decreased lacrimal gland secretion, conjunctival damage, or eyelid damage
  10. What is trachoma?
    An eye infection by Chlamydia trachomatis through direct contact of contaminated finger, fly, towel, etc to the conjunctiva
  11. What are the specific mechanisms that pathogens have evolved to invade a normal healthy respiratory tract w/ description AND examples
    • 1. attach firmly to surface of mucosal cells by using specific adhesion molecules
    • eg. Hemagglutinin on influenza virus to sialic acid on respiratory tract cells
    • 2. inhibit ciliary activity
    • eg. Bordatella pertussis (whooping cough) produces ciliostatic substances
    • 3. avoid phagocytosis or avoid destruction after phagocytosis
    • eg. Tubercle bacilli survive in the phagosome of alveolar macrophages by inhibiting phagolysosome formation
  12. Give examples of microbes that infect the large bowel and small intestine.
    • Large bowel: Shigella
    • Small intestine: most salmonellae, rotaviruses
  13. What are the factors involved in GI tract infection w/ explanation and examples?
    • Infection depends on balance between production and removal of bacteria in the intestine (is # of attached microbes enough to infect?)
    • eg. V. cholerae establishment on mucosal surface is sufficient
    • Shigella flexneri requires exploitation of inflammation response for infection
  14. Describe infection by Shigella flexneri.
    • Can only enter cells from basal surface
    • 1. Uptaken by M cells and invades local macrophages
    • 2. Infected macrophages induce inflammation which causes disruption of epithelial barrier
    • 3. Now many Shigella can enter from intestinal lumen and invade epithelial cells from below
  15. What are the mechanisms in the GI to counteract microbes w/ description
    • Mucus: protects GI epithelia with molecules that bind to microbial adhesins OR by secreted IgA (specific)
    • acids: most bacteria are acid sensitive (prefer slightly alkaline)
    • bile salts: detergents that are toxic to some bacteria
  16. What microbes can pass through the mucus layer in the GI tract? Why?
    • V.cholerae, salmonellae, and E. coli are motile and can propel themselves through the mucus layer to reach GI epithelia
    • V. cholerae secretes mucinase that degrades mucin
    • Non-motile microbes rely on random/passive transport through mucus layer
  17. Give a detailed account of Heliobacter pylori's defense mechanism and symptoms/disease
    • Attaches by adhesins to stomach wall and produces large amounts of urease which converts local urea to ammonia providing a buffer cloud
    • Induces apoptosis in gastric epithelial cell walls causing inflammation, dyspepsia, and sometime an duodenal or gastric ulcer
    • DO NOT invade tissues, but can stay in the stomach for years asymptomatically
    • May caused development of stomach cancer
  18. How can some bacteria escape death from bile acids?
    • Some have conjugated bile acid hydrolase (CBAH) to remove taurine AA from a cholic acid bile salt
    • Some have BaiA that removes a H from the cholica acid hydroxyl group
    • Both inactivate the bile acid
  19. Examples of organisms that can colonize vagina during reproductive life
    • lactobacilli (cause acidic environment from glycogen fermentation)
    • certain streptococci
    • diphtheroids
  20. Give a specific example of an attachment mechanism of a urinary tract invader
    • gonococci produce a peptide on the bacterial pili which binds to a syndecan-like proteoglycan on the urethral cell
    • The cell is the induced to engulf the bacterium
    • This is called parasite-directed endocytosis
  21. Describe oropharynx defenses from infection
    • Flushing action of saliva (1L/day)
    • Secretory IgA antibodies
    • Antimicrobial substances (eg lysozyme)
    • normal flora
    • leukocytes present on mucosal surfaces/ in saliva
  22. Describe the mechanisms of oropharyngeal infection including example organisms
    • Different streptococci make specific attachments via lipoteichoic acid molecules on the pili to the buccal (mouth) epithelium and tongue (resident Streptococcus salivarius)
    • to teeth (Streptococcus mutans)
    • to pharyngeal epithelium (invading Streptococcus pyogenes)