Micro

Question 1

N. meningitidis

Answer 1

• LOS, IgA protease, meningococcus capsule, porins, Opa
• gram(-) diplococci, aerobic/facultative, human-restricted, oxidase+, catalase+, ferments maltose
  
  • use thayer martin, chocolate agar if normally sterile site
• host defends with IgG-enhanced complement and PMNs; neonates protected by passive maternal immunity
• meningococcemia: septic arthritis, meningitis, endocarditis
• vaccine available
• treat w/ceftriaxone, NOT STEROIDS, admit if complication

Question 2

N. gonorrheae

Answer 2

• LOS, IgA protease, gonococcus pili, porins, Opa
• gram(-) diplococci, aerobic/facultative, human-restricted, oxidase+, catalase+,
• use thayer martin, chocolate agar if normally sterile site
• host defends with IgG-enhanced complement and PMNs (usually contains gonococcus)
  
  • prophylactic eye ointment for neonates
• asymptomatic/untreated→PID
• DGI: septic arthritis, meningitis, endocarditis
• treat w/ceftriaxone, NOT STEROIDS, admit if complication

Question 3

group B strep/s. agalactiae

Answer 3

• encapsulated gram+ ßhemolytic cocci; normal flora, opportunistic pathogen
• neonates: sepsis with pneumonia (early) or meningitis (late)
  
  • early disease prevented by intrapartum IV abx
• elderly with predispositions (esp. diabetes and CHF): cellulitis, meningitis, abscess, endocarditis.
• CAMP test: factor secreted with GBS that interacts with ßhemolysin of s. aureus→ enhanced hemolysis
• treat w/penicillin, amoxicillin, vanc

Question 4

strep pneumoniae

Answer 4

• gram+ catalase(-) diplococci , form chains in culture
  
  • carried in upper respiratory tract or vaccinated immune
• MCC of CAP, bacterial meningitis, bacteremia, and otitis media
• noninvasive disease: direct extension into sinuses, eustachian tubes, bronchi→sinusitis, otitis media, pneumonia
  
  • diagnose clinically, treat with amoxicillin
  • severe pneumonia: xray for lobar consolidation; admit for amoxicillin, fluoroquinolones, and/or vanc; do abx sensitivity testing
• invasive disease: hematogenous spread to meninges, joints, heart valves and strong inflammatory response
• LP: elevated opening pressure, elevated WBC (esp. neutrophils), elevated protein, low glucose, high lactic acid (fermenting glucose)
  
  • gram stain/culture are positive unless abx began >4hrs ago
  • treat w/ vanc plus ceftriaxome or cefotaxime
    
    • abx resistant (toxic MIC): add rifampin, meropenem, or chloramphenicol
    • Use steroid sparingly
• vaccination prevents invasive disease; Prevnar7 recently increased to Prevnar13 and may have to step up again (“replacement disease”)

Question 5

what are the routes of viral entry into the CNS?

Answer 5

• hematogenous
• olfactory
• neuronal

Question 6

what is meningitis and its defining clinical characteristics?

Answer 6

• inflammation of lining of brain
• headache, fever, chills, stiff neck, normal mental status​
  
  • Brudzinski’s sign
• 80% caused by enterovirus; other are HSV and arbovirus

Question 7

what is encephalitis and its defining clinical characteristics?

Answer 7

• inflammation of brain tissue, risk of intracerebral hemorrhage
• headache, fever, chills, stiff neck, mental status change
  
  • ​Brudzinski’s sign

Question 8

what CNS viral infections are spread neuronally?

Answer 8

• Herpesviruses (alphaherpesviruses): MCC sporadic viral encephalitis
  
  • ​MRI shows unilateral temporal lobe abnormalities
  • PCR of CSF
  • treat with IV acyclovir
• Rabies: post exposure immunization can prevent disease due to long incubation period
  
  • infects peripheral nerves and travels to brain→ hydrophobia, seizures, hallucinations, paralysis, coma

Question 9

what CNS viral infections are spread fecal-orally?

Answer 9

Picornaviruses (enteroviruses)

• more common in summer
• happens in young children and elderly
• no vaccines or antivirals except for polio

Question 10

what CNS viral infections are spread by insect vectors?

Answer 10

• Flaviviruses: JE, WNV, SLE
  
  • MC in summer
  • different tissue tropisms
• Togaviruses (Alphaviruses): VEE, EEE, WEE
  
  • ​usually cleared by macrophages and spleen/lymph nodes

Question 11

what test is necessary to determine the presence of meningitis?

Answer 11

• CSF
  
  • opening pressure: limited value if normal; usually high in bacterial
  • white count: >1000 cells in 90% of bacterial
    
    • neutrophils in bacterial
    • lymphocytes/monocytes if viral
  • protein: elevated in bavterial and fungal
  • glucose: low in bacterial, normal to minimally low in viral and fungal

Question 12

what is the gold standard for diagnosis of bacterial meningitis?

Answer 12

• culture
  
  • anaerobic culture may be important for postop or shunt meningitis
  • fungal and AFB require high volume taps
  • viral culture not indicated (do PCR)

Question 13

aseptic viral meningitis

Answer 13

absence of recognizable organisms in an illness with meningeal irritation, fever, and alterations of consciousness; usually rate limiting→lymphocytes, moderate protein elevation, normal glucose

Question 14

viral encephalitis

Answer 14

• Perivascular and parenchymal mononuclear infiltrates (lymphocytes, plasma cells, macrophages)
• Glial cell reactions (including formation of microglial nodules) and neurophagia
• Herpes: affects temporal and inferior frontal lobe→ necrosis→ hemorrhage
  
  • HSV1 in adults; HSV2 in newborns
• Progressive multifocal leukoencephalopathy (PML): JC polyomavirus infects oligodendrocytes→ demyelination (mimics MS)
  
  • occurs in immunosuppressed

Question 15

fungal meningoencephalitis

Answer 15

• Mucor and Aspergillus: associated with vasculitis
  
  • Mucor seen in diabetes
• Candida and Crypto: associated with brain invasion
  
  • Crypto: soap bubble appearance
• Toxo: free tachyzoites and pseudocysts with bradyzoites