MICROBIOLOGY REVISION Flashcards
purpose of BBB
protect against circulating toxins
allow vital nurtients to reach brain
helps maintain constant levels of water nutrients and hormones in brain
bacterial infection CNS
bind to the endothelial wall
causign tight junctions to slightly open
BBB becomes more porous
allows bacteria to infect the brain tissue, leading to inflammation and death
astrocytic end feet
cover almost entire surface of lbood vessel
regulate dilation and constriciton of microvessels to control blood flow
components of the BBB
tight junctions among endothelial cells, pericytes, astrocytic end feet
sequential pattern of acute bacterial meningitis pathogenesis
nasopharyngeal colonisation
bloodstream invasion across the mucosa
circulation of bacteria to the central nervous system (CNS)
subsequent CNS entry
colonisation of nasopharnyx in immunocompetent people
cleared by mucosal immunity
torjan horse
engulfing of the pathogen in the periphery
manipulation of the phagocyte to promote migration to brain or suppress phagocyte activaton
allows infected cell to circulate normally
adheres to luminal side of brain capillaries and crosses BBB
pathogen exits trojan horse to infect other neural structures
neisseria meningitidis staining
meningococcus
gram negative diplococcus
pathogenecity factors of neisseria meningitidis
type 4 pilus: mucosal colonisation
polysachharide capsule avoiding phagocytossis
LOS endotoxin
pilis mediated adhesion in neisseria meningitidis
induces formation of micro-villi like structures at the site of infection
trigger bacterial internalisation
reorganisation of actin cytoskeleton
forms membrane protrusions
engulfs bacteria into intracellular vacuoles
NMEC staining
neonatal meningitis e coli
extratintestinal e coli
gram negative bacillus
pathogenecity factors NMEC
K1 capsule
outer membrane protein A
type 1 pili
CNF-1 and IbeA for invasion
gold standard meningitis diagnosis
lumbar puncture of CSF sample
fluid may be turbid if bacteria present
within 1 hour of specimen collection CSF will be centrifuged to collect cell and cell debris
what happens if bacteria not visible
may be another cause
Or in small amounts so do a PCR test then re-evalutate
full meningitis diagnosis
Complete cell count (Total WBC ↑)
Differential leucocyte count (raised)
Examination of Gram-stained smear by microscopy
Culture usually onto Columbia blood agar and Chocolate agar or Thayer-Martin Medium
Determination of glucose (reduced) and protein (raised)concentrations
PCR where appropriate
Antigen testing (Latex Agglutination Test)
MALDI if available as more rapid results
