MedMicroTest3GramNegativeCocci

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victimsofadown
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MedMicroTest3GramNegativeCocci
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2013-11-02 01:55:18
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MedMicroTest3GramNegativeCocci
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  1. What are the general features of Neisseriae (gram reaction, aeration, shape/morphology, motility, capsulation, other structures?)
    • Gram-negative
    • Aerobic
    • diplococci
    • Nonmotile
    • Gonococci: unencapsulated
    • Meningococci: encapsulated in samples
    • Pili
  2. What are the two Neisseria species responsible for disease in humans?  Name of disease?
    • Neisseria gonorrhoeae (gonococcus): gonorrhea
    • Neisseria meningitidis (meningococcus): meningitis
  3. Where is N. gonorrhoeae typically found within clinical samples?
    Inside polymorphonuclear leukocytes (granulocytes)
  4. How is N. gonorrhoeae transmitted? Why?
    • During sexual contact (often)
    • From infected birth canal (infrequent)
    • *highly sensitive to dehydration
  5. What are the virulence factors in N. gonorrhoeae w/ description?
    • Pili: enhance attachment to mucosa and resist phagocytosis (only pilated species are virulent)
    • Antigentic variation - expression of varied  pilin molecules over time via pilin gene recombination
    • Lipooligosaccharide (LOS): similar to LPS, but is highly branched, and has an absence of repeating O-antigen subunits
    • Outer membrane proteins:
    • OMP I and III - Make a porin complex in the outer membrane
    • OMP II (opacity protein) - make colonies less translucent, mediates attachment to mucosa (with pili), and undergoes extensive antigenic variation
    • IgA protease: cleaves IgA1 (immunolgobulin)
  6. Where does N. gonorrhoeae typically colonize and what are its symptoms? (general)
    • Mucosa of the genitourinary tract or rectum
    • Typically causes localized infection with pus production immediately (acute infection)
    • May lead to tissue invasion, chronic inflammation, and fibrosis
    • Females are often asymptomatic and act as reservoirs for infection (chronic infection)
  7. What are the potential disease states caused by N. gonorrhoeae with a brief description/symptoms?
    • Genitourinary tract infections:
    • males - yellow, purulent urethral discharge.  Painful urination.
    • females - greenish-yellow cervical discharge.  Intermenstrual bleeding.  Infertility occurs in ~20% of women (tubal scarring).
    • Rectal infections: constipation, painful defecation, purulent discharge
    • Pharyngitis: purulent exudate, may mimic mild viral sore throat
    • Opthalmia neonatorum: infection of conjuntival sac at birth.  Could lead to blindness.
    • Disseminated infection: Septicemia is rare, but may result in fever, painful, purulent arthritis, and small pustules on the skin.
  8. What is the most common cause of septic arthritis in adults?  Children?
    • Adults: gonococcal infection
    • Children: S. aureus
  9. Describe the laboratory identification for N. gonorrhoeae (general, culture conditions, and tests)
    • Male - finding of neutrophils containing gram-negative diplocci in smear from urethral exudate (not specific)
    • Female - positive culture is required to diagnose.
    • Culturing conditions: aerobic conditions with CO2 present.  Cultures plated promptly for sample integrity. 
    • Thayer-Martin medium (choc. agar+antibiotics) selects for gonococci.
    • All Neisseria are oxidase-positive
    • N. gonorrhoeae ferments glucose only
  10. Describe the treatment of N. gonorrhoeae
    • >20% of isolates are resistant to penicillin, tetracylcine, cefotoxin, and spectinomycin
    • Most strains respond to 3rd generation cephalosporins
  11. When are meningitis outbreaks most common?  Why?
    • Winter and early spring due to close contact between individuals (schools, institutions, barracks)
    • Transmitted through respiratory droplets
  12. What are the virulence factors in N. meningitidis w/ description?
    • Capsule: antiphagocytic (most important)
    • Pili: allow attachment to the nasopharyngeal mucosa (exists as normal flora for 5-15%)
  13. How are N. meningitidis strains categorized?  What are the important types?
    • Serogroup: based on the LOS and capsule
    • Most infections caused by serogroups A,B,C,W, and Y
    • Serogroup A: responsible for massive epidemics (meningitis belt)
    • Serogroup B: most common in the US
  14. Describe the epidemiology of N. meningitidis (transmission, risk factors, hosts, and susceptible targets)
    • Transmission via inhalation of respiratory droplets (asymptomatic carrier or presymptom patient)
    • Risk factors: recent upper-respiratory tract infection, smoking, and complement deficiency
    • Humans are the only natural host
    • Incidence is highest amongst infants <1 year
  15. What are the potential disease states caused by N. meningitidis with a brief description/symptoms?
    • Initially colonizes nasopharynx (asymptomatic)
    • In young children organism penetrates epitehlia and spreads through blood (meningococcemia) causing meningitis and/or fulminating septicemia
    • purulent meningitis: crosses blood-brain barrier, infects meninges, induces inflammatory response
    • fulminating meningococcemia: rapidly moving septicemia w/o meningitis.  LOS causes skin hemorrhages, vomiting, diarrhea, circulatory collapse, and death within 10-12 hours (FAST)
    • Not severe: fever and nonspecific symptoms
  16. Describe the laboratory identification of N. meningitidis (general, culture conditions, and tests)
    • Appears of gram-negative diplococci in association with granulocytes under light microscope (from CSF)
    • Carriers detected by swabbing the nasopharynx
    • Culture conditions: chocolate agar (non-selective + blood) w/ increased CO2.  Usually cultured from CSF or blood (should be sterile ∴ selective media unneccessary.
    • Thayer-Martin medium required for nasopharyngeal swab
    • All Neisseria are oxidase-positive
    • Ferments glucose AND maltose
    • Rapid latex agglutination tests can ID serogroups
  17. What is the treatment for N. meningitidis
    • Medical emergency - antibiotic treatment CANNOT await definitive diagnosis
    • High fever, headache, and rash indicative of meningococcal infection are treated immediately.
    • Previous used penicillin G or ampicillin in large intravenous dose, but now use other antibiotics
  18. Describe the prevention of N. meningitidis
    • MCV4 vaccine: tetravalent vaccine for serogroups A, C, W-135, and Y conjucated to diptheria toxoid which increases effectiveness (limited to ages 11-55)
    • Prophylaxis: rifampin for family members of an infected individual eliminates carrier state

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