Bacterial CNS Infection Flashcards
gram-negative diplococci found in the upper respiratory tract
neisseria meningitidis
gram-negative rods found in the GI tract
escherichia coli (usually in young, elderly, and immunosuppressed)
gram-negative coccobacilli found in the upper respiratory tract
haemophilus influenzae (not seen very much because of effective vaccine)
gram-positive cocci in short chains found in GI tract and lower female genital tract
streptococcus agalactiae (GBS)
what type of hemolysis is expected with Group B Strep?
subtle beta hemolysis
gram-positive cocci in short chains found in the upper respiratory tract
streptococcus pneumoniae (can see “halo” of capsule, can differentiate based on positive P disk–optichin and alpha-hemolysis)
gram positive cocci in clusters found in skin, nares
staphylococcus aureus (also beta hemolytic, catalase +, coagulase +)
gram-positive facultative intracellular rods found in GI tract
listeria monocytogenes (can cause meningitis in children)
acid-fast bacillus in lower respiratory tract
mycobacterium tuberculosis
spirochete that disseminates from the urogenital tract
treponema pallidum (Syphilis)
spirochete transmitted by black legged ticks
borrelia burgdorferi (Lyme disease)
what are the 3 most likely causes of bacterial meningitis in newborns?
1) GBS, 2) E. Coli, 3) L. monocytogenes
what are the 2 most likely causes of bacterial meningitis in people >3mo old?
1) Strep pneumoniae, 2) N. meningitidis
what is opisthotonos, and what is it a sign of?
rigidity with arched back and head thrown backwards, seen in infants, sign of meningitis
where is the greatest risk of getting meningitis?
the meningitis belt in central Africa (meningococcal form)
when and why is meningococcal meningitis so common in central Africa?
dry season (cold nights, wind-blown dust) irritates the nasal and respiratory passages, increasing the risk of invasive disease in those already colonized by N. meningitidis
when were meningococcal polysaccharide vaccines first developed?
1969 by military doctors, basis of current bivalent and quadrivalent
what is different about the meningococcal vaccine that was developed in the last 10 years?
it is a conjugate vaccine that protects against 4 of the 5 major disease-causing serogroups (A,C,Y, and W-135)
what differs among the various meningococcal serotypes?
the polysaccharide capsule
which meningococcal serotype is not covered by the vaccine, and why?
the type B capsule, because it is made of carbohydrates similar to those found in the fetal brain (molecular mimicry - poor immunogen, concern for cross-reaction)
what distinguishes N. meningitidis from N. gonorrhea?
CAPSULE (otherwise looks very similar)
describe the pathogenesis of N. meningitidis?
1) adheres to non-ciliated epithelium, 2) internalized, 3) replicated intracellularly, 4) trancytosed thru BL tissue, 5) disseminates into blood
what type of skin lesions are seen with invasive meningococcal infections?
hemorrhagic skin lesions that are macular or non-blanching petechiae
how do meningococci invade the CNS?
high blood concentrations, bacteria cross BBB of meningeal blood vessels and enter subarachnoid space, then can enter lateral ventricles through choroid plexus –> proliferation and super high concentration in CSF
Brudzinski’s sign
severe neck stiffness causes a patient’s hips and knees to flex when neck is lifted off table (flexed) – sign of meningitis
Kernig’s sign
severe hamstring stiffness causes inability to straighten leg when hip is flexed to 90 degrees
describe the typical CNS profile for meningococcal meningitis
CSF is cloudy due to WBCs and bacteria, WBC highly elevated (1000-5000) with PMN predominance, decreased glucose (less than 1/2 serum level), elevated protein (>100)
what is a common virulence factor found in bacteria (and fungi) that cause meningitis?
most of them have polysaccharide capsules (N. meningitidis, E. coli, H. influenzae, S. pneumoniae, GBS, S. aureus, c. neoformans
name 4 non-encapsulated bacteria that infect the CNS
listeria monocytogenes, mycobacterium TB, treponema pallidum, borrelia burgdorferi
what 3 virulence mechanisms enable listeria to invade the CNS?
transport inside monocytes (Trojan Horse), direct invasion of endothelial cells, invasion of cranial nerves (by bacteria in oral macrophages) and retrograde movement into CNS
what virulence factor enables TB to get into the CNS?
it is maintained inside macrophages
what is unique about T. pallidum and B. burgdorferi that allows them to enter the CNS?
they are spirochetes whose corkscrew motility allows them to squeeze through the epithelium of the BBB
in what ways does listeria meningitis present atypically?
longer course, encephalitis-like symptoms, often no bacterial meningitis CSF findings, CSF gram stain shows no bacteria
describe TB meningitis
TB forms small foci in the meninges and brain parenchyma that can rupture and lead to inflammatory meningitis; TB invades microglia cells and can become walled off in spinal cord (Pott’s disease)
