Bacterial Infections of CNS Flashcards
Which menigeal layers become inflamed during bacterial infection?
pia mater and the arachnoid
List the primary pathogens of bacterial meningitis (4):
- Group B Streptococcus
- Streptococcus pneumoniae
- Neisseria meningitidis
- Haemophilus influenza
List the occasional pathogens of bacterial meningitis (7):
- Listeria monocytogenes (> 50 years of age)
- Escherichia coli and other Enterobacteriaceae
- Staphylococcus aureus
- Nocardia
- Mycobacterium tuberculosis (AIDS associated)
- Borrelia burgdorferi, Leptospira, Treponema pallidum
- Brucella
- Brain damage during meningitis is mostly attributable to ….
- Bacteria like Streptococcus pneumoniae cause that leads to tissue damage?
- Problem, early signs of meningitis can resemble the symptoms of:
- What is the key to curing infections?
- Brain damage during meningitis is mostly attributable to the side effects of the host’s own inflammatory response
- Bacteria like Streptococcus pneumoniae activate leucocytes
- release proteolytic enzymes and reactive oxygen species
-
Problem, early signs of meningitis can resemble the symptoms of:
- influenza
- altered mental status (confusion)
- Key: rapid diagnosis
Bacteria that cause CNS infection in:
Premature babies and newborns up to 3 months old
-
group B streptococci
- inhabit the vagina
- mainly a cause during the first week of life
- Escherichia coli
- normally inhabit the digestive tract
- carry the K1 antigen
- Listeria monocytogenes
Bacteria that cause CNS infection in:
Older Children
- Streptococcus pneumoniae
- Neisseria meningitidis
- Haemophilus influenzae type B
- in countries that do not vaccinate
Bacteria that cause CNS infection in:
Adults
-
Streptococcus pneumoniae and Neisseria meningitidis together
- 80% of bacterial meningitis cases
- Listeria monocytogenesis a risk in the elderly > 50 years
Which of the primary bacterial pathogens of the CNS does **not **have a vaccine?
Group B Streptococcus
(agalactiae)
- Most capsules are composed of ___________
- __________ antibodies prevent host cell phagocytosis
- Most capsules are composed of polysaccharides
- Anti-capsule antibodies prevent host cell phagocytosis
H. influenzae
- How many serotypes are there?
- Which one causes virtually all invasive infections?
- What plays a role in protection from infection?
- 6 serovars
- Virtually all invasive infections are due to type b H. influenzae (Hib)
- Antibodies to this polyribosylribose phosphate capsular antigen play a role in protection from infection by Hib
Describe the immunity to Hib:
- Good relationship between age & susceptibility
- Children < 3 month, maternal Abs are protective
- Most invasive disease occurs between 3 month and 3 years of age
- Children under 3 years of age show a humoral immunodeficiency to Hib
- Children older than 3 years of age develop bactericidal
- Ig to Hib (vaccination/non-clinical exposure)
What is the correlation between Hib meningitis and antibody titers?
Good correlation – incidence meningitis and antibody titers to the Hib capsule
- i.e. Incidence ↓ as antibody titer ↑
What was the problem with the 1st generation Hib vaccine?
Purified capsular polysaccharide
-
Polysaccharides are:
- poor immunogens
- stimulate T-independent Ab
- poor immunologic memory
What is the composition of the 2nd generation Hib vaccines?
PRP protein conjugates
Polysaccharide-conjugate vaccines stimulate a ….
T-cell dependent antibody response and a memory response
Neisseria meningitidis
- Gram stain
- Type of pathogen
- Responsible for …
- Gram (-) diplococci
- Intracellular, human-specific pathogen
- Responsible for septicemia and meningitis
Neisseria meningitidis
3 Virulence Factors
-
Lipooligosaccharide:
- component of the outer membrane (endotoxin) which stimulates TLR system
- fever, septic shock, and hemorrhage due to the destruction of red blood cells
- component of the outer membrane (endotoxin) which stimulates TLR system
-
Polysaccharide capsule:
- prevents host phagocytosis
- evasion of host immune response
-
Fimbriae
- mediate attachment of the bacterium to cells of the nasopharynx
Neisseria meningitidis
Diagnosis
-
Gold standard is to isolate Nm as Gram negative diplococci from cerebrospinal fluid (CSF)
- Culture CFS on chocolate agar plate
- Polymerase chain reaction (PCR) may also be sued to identify Nm
- What is the fatality risk for Nm?
- What should be done for patients with confirmed Nm?
- Fatality risk approaches 15% within 12 hours of infection, so initiate testing as quickly as possible, but do not to wait for the results before initiating antibiotic therapy
- Persons with confirmed Nm infection should be hospitalized immediately for treatment with antibiotics
Is Nm tranmissable?
Nm can be transmitted
- so contacts of the infected patient over the 7 days before onset should receive antibiotics to prevent secondary infections, especially young children
What are the serogroups of Nm and what vaccines have been developed for them?
- Nm comprise ~13 clinical serogroups classified by polysaccharide capsule
- **6 serogroups **
- A, B, C, Y, W135 and X
- responsible for virtually all cases in humans
-
Meningococcal conjugate vaccine (MCV4)
- preferred vaccine for < 55 years of age
-
Meningococcal polysaccharide vaccine (MPSV4)
- only meningococcal vaccine licensed for people > 55 (elderly)
What are the 2 general classifications of Streptococci?
-
β-hemolytic streptococci
- classified by Lancefield grouping
-
α-hemolytic and γ-hemolytic streptococci
- classified by biochemical testing
- a-hemolytic are referred to as viridans streptococci
- green pigment formed by the partial hemolysis of blood agar
Describe how Streptococci are classified based on hemolysis and cell wall components:
-
Hemolysis when grown on blood agar plates measure lysis of blood cells
- β clear (complete lysis)
- α green (partial lysis)
- γ none (no lysis)
-
Groups based on cell wall components = Lancefield typing scheme
- Group A = Streptococcus pyogenes (β hemolytic)
- Group B = Streptococcus agalactiae (β hemolytic)
- S. pneumoniae = No Lancefield group (α hemolytic)
Streptococcus pneumoniae
- Gram stain
- Shape
- Elongated gram (+)
- cocci arranged in pairs (diplococci) and short chains
**Streptococcus pneumoniae **
Virulence factors
- Ability to colonize oropharynx (surface protein adhesions)
- Spread into normally sterile tissues pneumolysin, IgA protease)
- Stimulate TLR inflammatory response (teichoicacid, peptidoglycan fragments),
- Evade phagocytic killing (polysaccharide capsule)
What can streptococcus pneumoniae cause?
- pneumonia
- sinusitis and otitis media
- meningitis
- bacteremia
What are the two Pneumococcal vaccines?
- PCV13
- PPSV23
What are the CDC recommendations for Pneumococcal vaccination?
-
Infants and Children younger than 2 Years of Age
- PCV13 is given to infants as a series of 4 doses,
-
Children 6 through 18 and older
- Vaccinate with conjugate vaccine
-
Adults 65 years of age and older (elderly)
- Vaccinate with PPSV23 vaccine
Group B streptococcus,
Streptococcus agalactiae
- Gram stain and classification
- Location of inhabitance
- Disease
- Gram positive, beta-hemolytic
- Lancefield typing scheme Group B
- Common inhabitant of pharynx, vagina
- Neonatal infections, meningitis
What is the treatment for Group B streptococcus, Streptococcus agalactiae
- No licensed vaccine
-
Penicillin is the drug of choice as a therapy
-
Selective prophylaxis antibiotics for Group B streptococcus
- Pre-term infants
- Early membrane rupture
- Previous infant with Group B streptococcal disease
-
Selective prophylaxis antibiotics for Group B streptococcus
