Name the four primary pathogens most often affiliated with bacterial meningitis
Group B Strep
What process drives most of the brain damage associated with bacterial meningitis?
The host's own inflammatory response (not the bacteria itself!)
Example; S. pneumoniae activates leukocytes that release proteolytic enzymes and ROS, damaging host tissue
Which pathogen(s) are most often affiliated with bacterial meningitis in:
Premature babies and newborns?
Premature babies and newborns: Group B streptococci, E. coli, Listeria
Older children: S. pneumoniae, N. meningitidis, H. influenzae (less of a problem now due to vaccination)
Adults: S. pneumoniae, N. meiningitidis, Listeria (>50 y.o.)
Is a conjugate vaccine available for:
Group B strep?
What about a polysaccharide capsule vaccine?
All four have an available polysaccharide capsule vaccine.
Give the gram stain and morphology of H. influenzae
G-, pleomorphic coccobacilli
Virtually all invasive infections of H. influenzae are attributable to what serotype?
Describe the composition of its polysaccharide capsule
What age group is most susceptible to infection?
Serotype B (Hib)
Capsule: ribose and ribitol
Children [3months, 3years]. Maternal antibodies are protective before 3 months, and children over 3 years will have developed humoral immunity to Hib.
What protein carrier was added in the second-generation Hib vaccine to give it greater immunogenicity?
Why is this superior?
conjugated PRP-D to Diphtheria toxoid
The carrier protein domain of the conjugated vaccine is internalized and processed by the B cell. It is then presented to a Th cell on MHCII. Actions of the T-cell induce memory.
Describe the three virulence factors of Neisseria meningitidis
Lipoligosaccharide: Component of the outer membrane (endotoxin). Stimulates the TLR system to produce fever, septic shock, and hemorrage (destruction of RBCs)
Polysaccharide capsule: prevents phagocytosis
Fimbriae: attachment to nasopharynx
Desribe the gram stain and morphology of N. meningitidis
What is the preferred growth medium for culture?
How else might it be identified?
Gram stain (gold standard) or PCR
Persons infected with N. meningitidis should be tested and treated (admit to hospital) as soon as possible. Why?
Who else should be notified/treated?
Fatality ~15% within 12 hours of infection
All contacts over the previous seven days should be identified/notified and receive antibiotic prophylaxis (especially children)
Asplenic children are especially susceptible to what form of bacterial meningitis? Who else is especially vulnerable to this pathogen?
Most common in infants <1yr or 16-21 y.o. (college students and military recruits)
Name the six serogroups of N. meningitidis that are responsible for virtually all human cases.
Describe the vaccination options
A, B, C, Y, W135
MCV4 (conjugate vaccine) - preferred for people <55y.o.
MPSV4 (polysaccharide vaccine) - preferred for people >55y.o.
Describe the hemolytic character of the following:
Group A strep
Group B strep
Give the gram stain and morphology of S. pneumoniae
Describe its virulence factors and their function(s)
G+ cocci in pairs and short chains
Surface adhesion proteins - colonize nasopharynx
pneumolysin - spread into normally sterile tissues
IgA protease - cleave IgA and spread into normally sterile tissues
teichoic acid - stimulate TLR inflammatory response
peptidoglycan fragments - stimulate TLR inflammatory response
polysaccharide capsule - evade phagocytic killing
Describe the vaccine options for S. pneumoniae, including their indications
PCV13 (conjugate vaccine): greater memory, but covers fewer serotypes. Indicated for infants <2y.o. and children 6-18y.o. and older (so... adults?).
PPSV23 (polysaccharide capsule): less memory, more serotypes covered. Indicated for adults >65y.o.
Is a vaccine available for S. agalactiae?
Give its gram staining, morphology, hemolysis, and Lancefield group
In what population(s) is infection with this organism especially concerning?
What mucosal surfaces usually harbor this bug?
G+ cocci, beta-hemolytic, Group B
Full-term infants (2-8% mortality) and pre-term infants (up to 30% mortality)
Commonly inhabits the pharynx and vagina (transmission risk to infants during birth?)
What is the preferred therapy for S. agalactiae infection?
Who should be given antibiotics prophylactically against this bug?
Prophylaxis: pre-term infants, pregnant women with early membrane rupture, pregnant women with previous Group B streptococcal disease