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2013-10-08 21:44:00

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  1. What are the relevant gram positive rods in med micro?
    • Corynebacterium diptheriae
    • Bacillus anthracis
    • Bacillus cereus
    • Listeria monocytogenes
    • Propionibacterium acnes
    • Lactobacillus
    • Erysipelothrix rhusiopathiae
  2. General features of Corynebacteria? (gram, shape, motility, capsulation, sporulation, aeration)
    • Gram+
    • small, slender rods that tend to stain unevenly
    • nonmotile
    • unencapsulated
    • do not form spores
    • facultative anaerobe (grow aerobically on lab media)
  3. Describe the epidemiology of Corynebacterium diptheriae.
    • Found in throat/nasopharynx of both carriers AND those with diptheria
    • Diptheria is a local infection of the throat
    • Commonly spread by respiratory droplets
    • Can be spread by direct contact or contaminated fomite
  4. Describe the pathogenesis of Corynebacterium diptheriae including mechanism of action
    • Diptheria is caused by the effects of a single exotoxin (diptheria toxin), which inhibits eukaryotic protein synthesis
    • Fragment B binds to cell membrane and mediates delivery of Fragment A
    • Fragment A separates and causes adenylation of EF-2, rendering it inactive
    • Production of diptheria toxin is a result of phage conversion
  5. Describe the potential diseases/infections that can result from Corynebacterium diptheriae
    • 1. Upper respiratory tract infection
    • Main infection
    • Strictly local infection
    • Produces thick gray pseudomembrane in throat WITHOUT PUS
    • Often causes marked swelling of the lymph nodes in neck
    • Untreated, the toxin can affect the heart and peripheral nerves
    • 2. Cutaneous diptheria
    • Caused by introduction of bacteria to subcutaneous tissue
    • Nonhealing ulcur with gray membrane (of skin)
  6. What symptoms should prompt consideration of Corynebacterium diptheriae?
    • Pharyngitis
    • Low-grade fever
    • Cervical adenopathy (neck swelling)
    • Erythmia of pharynx up to gray pseudomembrane of pharynx
  7. Describe the laboratory identification of Corynebacterium diptheriae.
    • Requires isolation of the organism and testing it for virulence (testing for diptheria toxin)
    • Isolated most easily on Tinsdale's agar where it produces black colonies.
    • Has distinctive banding when gram stained
  8. Describe the treatment and prevention diptheria?
    • Prevention by the DTP vaccination would be prefereable, but if infection occurs...
    • 1. Neutralization of toxin (horse serum antitoxin)
    • 2. Erradication of organism (erythromycin, penicillin)
  9. General features of Bacillus? (gram, shape, sporulation, aeration, common locations)
    • Gram+
    • blunt-ended bacillus
    • form endospores
    • stricty or facultatively aerobic
    • Most are found in soil/water
    • found as airborne contaminants in med labs
  10. Describe the epidemiology of Bacillus anthracis
    • enzootic disease of domestic sheep, goats, and horses transmitted to humans by contact with infected animal products or contaminated dust
    • Majority of infections initiated by subcutaneous spore introduction through broken skin
    • Less common infections initiated by inhalation of spores
    • **spores may remain viable for years in pastures, wool, hair, hides, etc
  11. Describe the pathogensis of Bacillus anthracis
    • The capsule (poly-D-glutamic acid) of B. anthracis is essential for full virulence
    • Produces three exotoxins...
    • 1. Edema factor (EF): causes elevation of intracellular cAMP, responsible for severe edema
    • 2. Lethal factor (LF): responsible for tissue necrosis
    • 3. Protective antigen (PA): mediates cell entry for LF and EF
  12. Describe the potential diseases/infections that can result from Bacillus anthracis
    • 1. Cutaneous anthrax
    • 95% of human cases
    • Malignant pustules evolve on skin
    • Untreated organisms may result in fatal septicemia (~20%)
    • 2. Pulmonary anthrax (woolsorter's Disease)
    • Caused by inhalation of spores
    • Results in progressive hemorrhagic lymphadenitis (inflammation of lymph nodes)
    • Mortality rate ~100% if untreated
  13. Describe the Laboratory identification of Bacillus anthracis
    • Microscopically appear as blunt-ended bacilli singly, in pairs, or in long chains
    • Do not sporulate in clinical samples, but do so in culture
    • Large, grayish, nonhemolytic colonies on blood agar
    • Can be distinguished from other Bacillus due to nonmotility and capsulation in vivo
    • Direct immunofluorescence assay aids in ID
  14. Describe the treatment and prevention of Bacillus anthracis
    • Sensitive to a variety of antibiotics (Penicillin not recommended)
    • Multidrug therapy is recommended for inhalation anthrax
    • Prevention: vaccine is available ONLY to workers in high-risk occupations
  15. Give information about Bacillus cereus
    • Implicated in opportunistic lesions (after trauma, catheters, etc)
    • Produces tissue-destructive extotoxin
    • Causes food poisoning by means of enterotoxins
  16. General features of Listeria (gram, shape, sporulation, biochemical properties, motility, special properties)
    • Gram+
    • Very short/slender rods (confused with coccus)
    • Non spore-forming
    • catalase-positive
    • distinct tumbling motility (actin-polymerization)
    • Salt tolerant
    • Survive/grow below 1C
    • L. monocytogenes is a model organism for intracellular pathogens
  17. Describe the epidemiology of Listeria monocytogenes
    • Listeriosis is usually foodborne (2-3% processed dairy products, 20-30% ground meats, majority of poultry are contaminated)
    • Growth at 4C ∴ refrigeration does not suppress
    • Listeriosis is most common in pregnant women, fetuses, newborns, the elderly, and the immunocompromised
  18. Describe the pathogenesis of Listeria monocytogenes
    • facultative intracellular parasite
    • Enters cells by normal phagocytosis
    • Hemolysin Listeriolysin O allows escape from the phagosome
    • Grows in the cytosol, and induces polymerization of cellular actin to create a "tail" which propels it
    • Transferred directly between adjacent cells
    • Hemolysin phospholipase C allows escape from the double-membraned vacuole formed after cell-cell passage
    • This process allows avoidance of intercellular milieu
  19. Describe the potential diseases/infections that can result from Listeria monocytogenes
    • Septicemia and meningitis are most common
    • Preggos may have mild flulike illness
    • Can be transmitted to newborn from vagina (meningitis) OR to the fetus from the placenta (abortion)
  20. Describe the laboratory identification of Listeria monocytogenes
    • Can be isolated from blood, CSF, etc
    • Blood agar: small colony surrounded by narrow zone of weak β hemolysis (better observed by removing colony)
    • Distinguished from streptococci by morphology, motility, and catalase production
  21. Describe the treatment and prevention of Listeria monocytogenes
    • Variety of antibiotics are available to treat infection
    • Proper food preparation and handling can prevent infection
  22. Give information about Propionibacterium
    (spores? aeration? gram? shape/morphology? information)
    • Non spore-forming, Anaerobic/microaerophilic, Gram + rods of diptheroid-like morphology
    • Common inhabitants of normal skin
    • rarely associated with endocarditis or plastic implant infections
    • P. acnes (strict anaerobe) is cause of acne
  23. Give information about Lactobacillus (spores? gram? shape? information)
    • non-spore forming, gram+, rods
    • Part of commensal flora of human mucous membranes
    • Produce large quantities of lactic acid during fermentation (maintain acidic pH)
    • May play a role in dental carries
  24. Give information about Erysipelothrix rhusipathiae (spores? gram? shape? information)
    • non-spore forming, gram+, filamentous rod
    • Causes disease in animals
    • Rarely associated with erysipeloid (a skin condition) in those who commonly handle animal products (eg butchers, vets, fisherman)