export_cns bacteria i Flashcards
Two main categories of CNS infections
Meningitis (affect meninges)
Encephalitis (affect brain parenchyma)
What makes up the blood brain barrier (BBB)?
Tight junctions between endothelial cells of cerebral microvasculature, epithelial cells of choroid plexus, and arachnoid cells
What does the BBB do?
Separates blood and CSF, isolating the CNS from the rest of the body
How do pathogens gain entry into the CNS?
Hematogenous spread from distant site of inoculation or infection (bacteremia)
Spread from adjacent/contiguous site to CNS
Direct inoculation
Neuronal spread
What is meningitis?
Inflammation of the meninges and CSF
What are the causes of meningitis, and which is the most severe?
Acute pyogenic (bacterial) - most severe Aseptic (viral)
Chronic (any class of microbe)
Increased risk for meningitis
Pneumonia or chronic otitis media (pneumococcal)
URTI (meningococcal)
Virulence factors for meningitis
Capsule
Fimbriae
Pili
MOMPs
Pathology of meningitis
Inflammatory mediators initiated due to toxins, resulting in edema, increased intracranial pressure, seizures, coma, and DEATH
Diagnose meningitis
Almost all patients have two of the following Sx:
Fever
Headache
Stiff neck
Altered mental status
Labs: CSF Gram-stain, cultures, latex agglutination
CSF abnormalities in bacterial meningitis
Presence of PMNs
Decreased glucose
Increased protein
Increased pressure
CSF abnormalities of viral meningitis/encephalitis
Monocytes and lymphocytes
Normal glucose
Normal/slightly increased protein pressure
Treatment of bacterial meningitis
Empirical antibiotic therapy
Using diagnostic tests can help determine most effective drug
Bacterial meningitis causative agents
S. pnuemo
N. meningitidis
S. agalactiae
Listeria monocytogenes
H. influenzae
S. pneumo features
Gram-positive cocci in chains
Catalase negative
Alpha-hemolytic
Susceptible to optochin and bile
What is the most common cause of vaccine-preventable death in the U.S.?
Pneumococcal meningitis
Pneumococcal virulence factors
Choline binding proteins
Pneumolysin
IgA protease
Capsule
Choline binding proteins
Allows for colonization in the oropharynx
Pneumolysin
Inhibits mucociliary clearance
May also interfere with macrophage clearance
Pneumococcal meningitis clinical importance
Acute onset
High mortality
Neurological sequela
Pneumococcal meningitis recommended therapy
Vancomycin with a cephalosporin
Modify when organism is identified
Pneumococcal polysaccharide vaccine (PPV)
Capsular polysaccharide Ag from 23 types of pneumococcus
Does not prevent pneumonia as effectively
Who should get the PPV?
Adults > 65 years old
Anyone > 2 years old with increased risk
Pneumococcal conjugate vaccine (PCV13)
Pneumococcal capsule (13 serotypes) conjugated to nontoxic diphtheria toxin
Who should get the PCV13?
Routine child vaccine
2, 4, 6 months, then booster at 12-15 months
N. meningitides features
Gram-negative diplococcus
Oxidase and catalase positive
Oxidizes BOTH glucose and maltose
Fastidious, requiring CO2
N. meningitides virulence factors
Capsule
LOS
N. meningitides transmission
~10% of population is colonized
Transmission is via aerosolized droplets
Which serotypes cause almost all invasive meningococcal disease?
C
B
Y
W-135
A
N. meningitides virulence factors
Pilli
Capsule
LOS
LOS effects
Inflammation/immune response
Endotoxemia (organ failure)
DIC
N. meningitides entry into CNS
BBB weakened
Cross BBB WITHIN neutrophils
What is meningococcemia?
Bloodstream infection occurring with or without meningitis
Meningococcemia Sx
Fever
Petechial/purpuric rash
Hypotension
Multiorgan failure
What causes meningococcal meningitis?
Hematogenous dissemination
Diagnose meningococcal meningitis
Gram-stain of CSF and/or blood
Bacteremia
Susceptibility testing
Treatment for meningococcal meningitis
Again, start with vancomycin and a cephalosporin until identification has occurred
N. meningitides is usually susceptible to penicillin, so can use this after identification
Meningococcal polysaccharide vaccine (MPV)
Tetravalent polysaccharide vaccine against serotypes A, C, Y, and W-135
Protection against B is on the way
Who should get the MPV?
Not recommended as routine vaccination, but should be used in high-risk persons
In event of an outbreak
What defines a meningococcal outbreak?
3+ cases in < 3 months
Meningococcal conjugate vaccine (MCV4)
Tetravalent against A, C, Y, and W-135 (B still on the way)
Conjugated to nontoxic diphtheria toxin subunit
Who should get the MCV4?
Anyone 11-55
9 months-55 years that have increased risk factors
Differences between MPV and MCV4?
MCV4 illustrates a booster effect, and has a higher IgG response, and a higher affinity Ab response
