1 Meningitis and Group A Streptococcal Flashcards Preview

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Flashcards in 1 Meningitis and Group A Streptococcal Deck (22):
1

The four most common causes of bacterial meningitis are encapsulated organisms. What are they:

  1.  (gram positive (gm +) diplococci)
  2.  (gm – diplococcus)
  3.  (gm+ cocci in chains)
  4.  (gm – coccobacillus)

  1. Streptococcus pneumoniae (gram positive (gm +) diplococci)
  2. Neisseria meningitidis (gm – diplococcus)
  3. Group B Streptococcus (gm+ cocci in chains)
  4. Haemophilus influenzae Type B (gm – coccobacillus)

2

  • Risk Factors - Associations with specific bacteria
    • Terminal compliment pathway deficiency

Terminal compliment pathway deficiency ‐ meningococcus

 

3

  • Risk Factors - Associations with specific bacteria
    • Cochlear implant, CSF leak

Cochlear implant, CSF leak – pneumococcus

 

4

  • Risk Factors - Associations with specific bacteria
  • Absence of opsonizing antibody

Absence of opsonizing antibody ‐ pneumococcus, H. influenzae

5

  • Risk Factors - Associations with specific bacteria
    • Corticosteroid use (high dose)

Corticosteroid use (high dose) - Listeria, Cryptococcus

 

6

  • Risk Factors - Associations with specific bacteria
    • HIV

  • HIV – pneumococcus, Cryptococcus, Listeria
  • – (Common feature is low CD4 cell count for corticosteroids and HIV)

7

Recent otitis media or respiratory infection

pneumococcus and H. influenzae

8

Injection drug use

Staphylococcus aureus

9

  • Mechanism of entry varies for each organism
    • Neisseria meningitidis:

  • Neisseria meningitidis: oropharyngeal colonization with pathogenic strain

10

  • Mechanism of entry varies for each organism
    • Streptococcus pneumoniae

  • Streptococcus pneumoniae: nasopharynx, (children) direct extension across skull fracture, spread from contiguous (otitis media) or distant site (pneumonia) (children and adults)

11

  • Mechanism of entry varies for each organism
    • Haemophilus influenzae

  • Haemophilus influenzae: nasopharynx, (children) spread from contiguous or distant site (children and adults)

12

  • Mechanism of entry varies for each organism
    • Listeria monocytogenes

  • Listeria monocytogenes across placenta or food borne. Occurs in neonates and elderly, HIV, pregnant women

13

  • Mechanism of entry varies for each organism
    • Coagulase negative Staphylococci

  • Coagulase negative Staphylococci: foreign body (CSF shunt)

14

  • Mechanism of entry varies for each organism
    • Staphylococcus aureus:

  • Staphylococcus aureus: foreign body, spread from bacteremic source (IVDU, skin, endocarditis), contiguous source (epidural abscess)

15

  • Mechanism of entry varies for each organism
    • Gp B Streptococcus:

  • Gp B Streptococcus: Bacteremia from GI or GU tract

16

  • Bacterial Meningitis Pathogenesis
    • Adherence factors - Which bugs
    • Polysaccharide capsule - Which bugs

  • Adherence factors (pili in meningococcus, adhesion molecules in pneumococcus) allow colonization Invasion of blood stream
  • Polysaccharide capsule (also used to identify serotypes in pneumococci, meningococci and H. influenzae) enable avoidance of phagocytosis by neutrophils and lysis by compliment factors
  • Invasion of meninges allows for rapid growth of organisms because of inadequate humoral immunity past the blood brain barrier (low immunoglobulin and compliment levels)

17

  • Etiologies:
  • Neonates:
  • Children:
  • Adults:

  • Neonates: E. coli and Group B streptococci, Listeria
  • Children:  Group B streptococci (37.8%: 85% of whom were under 2months). Pneumococcus (34%)
  • Adults:  Pneumococcus (71%), meningococcus (12%)
  • Listeria monocytogenes in pregnant women and elderly (4%)

18

  • Culture characteristics of main pathogens
    • – Streptococcus pneumoniae

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19

  • Culture characteristics of main pathogens
    • – Neisseria meningitidis

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20

  • Culture characteristics of main pathogens
    • H. influenzae

  • Small pleomorphic gram negative rod.
  • Oxidase positive, facultative anaerobes.
  • Requires hemin (factor x) and NAD (factor v) for growth.
  • Use chocolate (hemoylsed blood) agar to grow.
  • Capsulated and non capsulated (nontypable).
  • May have beta lactamase that inactivates ampicillin

21

  • Culture characteristics of main pathogens
    • Listeria monocytogenes:

  • Beta hemolytic gram positive rod.
  • Aerobic and facultatively anaerobic.
  • Motile.
  • May be gram variable and can be confused with S. pneumoniae, H. influenzae and diphtheroids

22

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