Bacterial Meningitis

Question 0

Conditions that Predispose Patients to Bacterial Meningitis

Answer 0

• Age-very young; very old
• Immunocompromised state
• Basal skull fracture
• Head trauma, post neurosurgery
• Cerebrospinal fluid shunt

Question 1

Most Frequent Causes of Bacterial Meningitis in the US:

Answer 1

Streptococcus pneumoniae 58% 
Group B streptococcus 18% 
Neisseria meningtides 14% 
Haemophilus infuenzae 7% 
Listeria monocytogenes 3%

Question 2

pathogenesis & clinical presentation of bacterial meningitis

Answer 2

• Hematogenous delivery of bacteria to subarachnoid space
• Host immune response
• Edema
• Increased intracranial pressure
• Decreased cerebral blood flow
• Damage, seizures, herniation
• Clinical Presentation
  
  • Headache ≥ 90
  • Fever ≥ 90
  • Meningismus ≥ 85
  • Altered sensorium > 80
  • Kernig’s sign ≥50
  • Brudzinski’s sign ≥ 50

Question 3

General diagnosis of bacterial meningitis

Answer 3

CSF:
*White blood cell count ≥1,000 per mm3 
Cell differetial  Mostly  PMNs 
Protein  Mild to marked elevation 
CSF-to-serum glucose ratio Normal to marked decrease

Question 4

Diagnosis of Meningococcal Meningitis

Answer 4

• meningococci in blood.
• May occur with or without:
  
  • petechiae and/or purpura
  • Waterhouse-Friderichsen syndrome
  • chronic recurring meningococcal disease.
• Gram-negative cocci
• Oxidase Positive

Question 5

Diagnosis of Group B streptococcal Meningitis

Answer 5

• Gram-positive cocci
• catalase negative
• Usually beta hemolytic
• bacitracin insensitive
• group B-specific cell wall antigen

Question 6

Diagnosis of Listeria monocytogenes Meningitis

Answer 6

Gram positive aerobic rod.

Question 7

General traits of Neisseria species

Answer 7

• Morphology: Gram-negative cocci occur in pairs
• Oxidase positive – have cytochrome C oxidase
  
  • measured by reduction of a dye to a blue color
• All are aerobic but will multiply under microaerophilic conditions
• Sugar Reactions Determines Species of Nesseria

Question 8

Traits of Listeria monocytogenes

Answer 8

• Gram positive aerobic rod.
• Grows at cold temperatures or mesophilic (moderate temps)
• Widely distributed in nature.
• Facultative intracellular pathogen
• Produces listerolysin (LLO)
  
  • promotes release of bacteria from phagosomes into cytoplasm

Question 9

Epidemiology of various serogroups of Neisseria meningitidis in the U.S. vs the developing world

Answer 9

-Spread: human to human.
*Asymptomatic carrier = focus of infection.
Age: incidence greatest b/t 6 months & 3 years in unvaccinated
-Serogroup- incidence varies w/ serogroup & location of outbreak.
-Serogroup A causes epidemics in less developed nations
-In US, Groups B and C most often cause meningitis
-Africa, group A and W-135.
Serogroup A=one clonal serotype and that serogroups B and C have multiple serotypes.

Question 10

Virulence Factors of Neisseria meningitidis

Answer 10

• Capsules are Key Virulence Determinants
• Antiphagocytic: interfere w/ complement deposition
  
  • prevent C3b-mediated uptake of meningococci by phagocytes.
• 12 serogroups: Antibodies to type B capsule cross-react with E. coli-1 capsule
• Antibodies against capsular polysaccharide are bactericidal in the presence of complement
• LOS (lipooligosaccharide): toxic properties of the meningococcus reside in its LOS

Question 11

Virulence factor in Group B streptococci

Answer 11

capsules = virulence factor

Question 12

Virulence Factors for Listeria monocytogenes

Answer 12

• Listeriolysin O: required to escape vacuole & multiply in cytoplasm of cells
  
  • promotes release of bacteria from phagosomes into cytoplasm
• LLO responsible for hemolytic phenotype of L. monocytogeneson blood agar plates

Question 13

meningococcal vaccines

Answer 13

• Tetravalent conjugate vaccine licensed for use in the US in 2005
• Called MCV4: capsular polysaccharide from A, C, Y, & W135
  
  • each conjugated to diphtheria toxoid.
• Two dose of MCV4 is recommended for all 11-16 year-olds
• Vaccination with MCV4 also recommended for unimmunized persons (ages 2-55) who are at increased risk
  
  • college freshmen living in dormitories
  • microbiologists routinely exposed to isolates of N. meningitids
  • military recruits
  • travelers/residents of countries where N. meningitidis epidemic
  • persons with terminal complement component deficiencies
  • anatomic or functional asplenia.

Question 14

Describe how L. monocytogenes moves from cell to cell

Answer 14

After bacteria escape from phagosomes, multiply in cytoplasm

• Move w/in cells by a mechanism that involves host actin polymerization meditated by ActA
• Bacteria then spread directly from cell to cell without re-entering the extracellular space.
• Actin acts as ‘rocket tail’ allowing it to propel to next cell w/o entering extracellular space

Question 15

diseases caused by Listeria monocytogenes

Answer 15

• Food-borne pathogen (e.g., soft cheese, lunch meats, hot dogs )
• can cause miscarriage and stillbirths in pregnant women
• severe systemic disease in the immunosuppressed
• occasionally, gastroenteritis in healthy people