2.4 Acute Bacterial Meningitis Flashcards
How can pathogens infect the CNS?
- Hematogenously
- Peripheral nerves
- Olfactory neurons
- Local injury or congenital defect
- Pathogens transverse the blood brain barrier
What are the three ways that pathogens can transverse the BBB?
- Transcellular traversal: Through the cell
- Paracellular traversal: between cells
- Trojan horse mechanism: Macrophage
What is meningitis?
infection of the meninges after crossing blood-CSF barrier
What is encephalitis?
infection of the cerebral cortex after crossing the BBB
What is Myelitis?
Infection of the spinal cord, usually by viruses
What is post infectious encephalitis?
Usually 2-3 weeks after an infection elsewhere in the body, peripheral immune cells gain access to brain through BBB
What are defining characteristics of bacterial meningitis?
- May be preceded by upper respiratory tract or ear infection
- Growth in CSF initially unimpeded, then attracts PMNs, which lyse to release toxic factors leading to necrosis and edema, and reduced glucose transport in the arachoid & pia matar.
- Thus, the CSF will have a high level of leukocytes, primarily neutrophils & a low level of glucose.
- Inflammation impedes CSF flow leading to cerebral edema, hypoxia of the cerebral cortex & irreversible ischemic damage
What are the normal symptoms of bacterial meningitis in children and adults?
- Fever, headache & nuchal rigidity
- Altered mental status
- Brudzinski or Kernig sign present
- Loss of consciousness
- Purulent nasal discharge
- Grand mal or focal seizures
- Focal neurological findings
- May progress to coma and/or death
What are the symptoms of bacterial meningitis in infants and neonates?
- Fever, lethargy & irritability
- Poor feeding
- High-pitched cry
- Respiratory distress
- Bulging fontanelle
- Hypotonia
- Jaundice
- Rash
- Seizures
What bacteria are most likely in meningitis of age 0-4 weeks?
- Step agalactiae (GBS)
- Escherichia coli
- Listeria monocytogenes
What bacteria are most likely in meningitis of age 4-12 weeks?
- S. agalactiae
- E. coli
- H. influenzae
- S. pneumoniae
- N. meningitidis
What bacteria are most likely in meningitis of age 3 months to 18 years?
- N. meningitidis
- S. pneumoniae
- H. infuenzae
What bacteria are most likely in meningitis of age 18-50 years old?
- S. pneumoniae
- N. meningitidis
- H. influenzae
What bacteria are most likely in meningitis of age greater than 50 years old or immunocompromised?
- S. pneumoniae
- N. meningitidis
- L monocytogenes
- Aerobic Gram-negitive bacilli
What does a bacterial CNS infected CSF profile look like?
- Opening pressure: Elevated
- Clarity: Turbid; may clot
- Protein: Increased
- Glucose: decreased
- CSF: Serum glucose ratio less than 0.3
- WBC: increased
- Gram stained, acid fast, India ink: Shows organisms in about 75% of untreated cases
- Culture: Organisms grow in 85% of untreated cases
What are the age risk factors for bacterial meningitis?
-infants are at higher risk for bacterial meningitis than people in other age groups; vaccines have “pushed” the disease to adults instead of children
What are the community setting risk factors bacterial meningitis?
College students living in dormitories and military personnel are at increased risk for meningococcal meningitis
What recent disease risk factor does bacterial meningitis?
Recent upper respiratory tract infection or ear infection
What other risk factors are there for bacterial meningitis?
- Weakened immune system due to certain diseases, medications, or surgical procedures
- Working with meningitis-causing pathogens
- Travel to the meningitis belt in sub-Saharan Africa or to Mecca during the annual Hajj and Umrah pilgrimage
What are general characteristics of Steptococcus pneumoniae?
- Gram-positive cocus
- Diplococci or short chains
- Facultative anaerobic
- Encapsulated
- Optochin sensitive
- Bile-soluble (cells are lysed) whereas all other α-hemolytic streptococci are bile-resistant
- Mixing a suspension of pneumococci with type-specific antisera increases the visibility of the capsule in the microscope, and is the basis of the quellung reaction or capsular swelling test
Is Steptococcus pneumoniae catalase positive or negative?
- Negative catalase
What is the hemolytic type of Steptococcus pneumoniae?
-Alpha-hemolytic
What is disease does Steptococcus pneumoniae?
- Otitis media
- Pneumonia*
- Bacteremia/sepsis
- Meningitis
When does the most occurrences of Steptococcus pneumoniae occur?
• More common during the winter and early spring.
What is transmission routes of Steptococcus pneumoniae?
- Inhabitant of oropharynx and nasopharynx
- Direct person-to-person transmission via respiratory droplets is rare
- Humans only reservoir
What are the virulence factor of Steptococcus pneumoniae?
- Polysaccharide capsule
- Antiphagocytic by inhibiting complement deposition and phagocytosis when type-specific opsonic antibody is absent
- > 90 known serotypes based on capsular polysaccharides
- IgA protease
- Pneumolysin
* A cholesterol-dependent cytolysin that creates pores in cholesterol-containing membranes, thus causing host cell lysis
How do you diagnosis Streptococcus pneumoniae?
- Isolated from specimens of CSF
* Latex agglutination test
How do you diagnosis treatment?
- Up to 15% of invasive pneumococcal isolates are resistant to penicillin in some parts of the U.S
- Vancomycin combined with ceftriazone is used commonly for empiric treatment, followed by monotherapy with an effective cephalosporin, fluoroquinolone or vancomycin
What are the general characteristic of Streptococcus agalactiae?
- Spherical, Gram-positive cocci in chains
- Catalase-negative
- CAMP-positive = enhanced hemolysis in the presence of Staphylococcus aureus
- Bacitracin Resistant
What diseases Streptococcus agalactiae?
- Bloodstream infections
- Pneumonia
- Skin & soft-tissue infections
- Bone & joint infections
- Sepsis
- Meningitis (rarely)
Where does commensal normally Streptococcus agalactiae?
- GBS asymptomatically colonizes the lower gastrointestinal and genitourinary tracts
- Not harmful in nonpregnant women, and is a dynamic condition as GBS may come and go over months
