CNS infections Flashcards
(37 cards)
What is the most common method of entry of bacteria into the CNS?
Bloodborne invasion
What is encephalomyelitis?
Inflammation of spinal cord
What is meningoencephalitis?
Inflammation of the brain and meninges
What makes the junctions of the blood brain barrier vs blood-CSF barrier?
BBB - tightly joined endothelial cells surrounded by glial processes (i.e. astrocytes)
BCB - endothelial cells with fenestrations and tightly joined choroid plexus epithelium
What are the three ways in which microbes can cross the BCB or BBB?
- Infecting cells which comprise the barrier
- Being passively transported across in intracellular vacuoles
- Being carried across by WBCs
How do LPS and Techoic Acid increase the chances that the microbe will get into the CSF?
Cause inflammation. Cytokine release can cause an edema which allows immune cells to flow out of the bloodstream and into the CSF
What causes the CSF to become visibly turbid?
Increases in PMNs and proteins
What are examples of normal microbes / normal flora inhabiting mucosal surfaces which are the common cause of meningitis?
Strept pneumoniae -> found in Upper Respiratory Tract
N. meningitidis - found in URT and pharynx
H. influenzae - found in URT
Group B strept - found in GI tract
E. coli K1 - Found in GI tract and UG tract
What happens to protein, glucose, and WBC’s in CSF during bacterial meningitis?
Protein goes up
Glucose goes down (bacteria eat it)
WBC goes up (>50% are PMNs)
What happens to protein, glucose, and WBC’s in CSF during aseptic meningitis?
Aseptic = viral Protein goes up only slightly Glucose remains the same WBC goes up (not as much as bacterial) Less than half of WBC will be PMNs, except early on in disease course
What patient population normally has WBC and protein in the CSF?
Normal neonates have small amounts
What are the two forms of acute bacterial meningitis?
- Meningeal bacterial infection
2. Infections causing inflammation of meninges without infection in CSF
What are the symptoms of acute bacterial meningitis? What is indicative of a very severe infection?
Sudden: high fever, severe / persistent headache, “nuchal rigidity”, nausea, and vomiting
Severe: confusion, sleepiness, and difficulty waking up
What is the primary cause of bacterial meningitis in the US?
Streptococcus pneumoniae
How is S. pneumoniae spread, and what is its morphology / lab identification?
Aerosols or direct contact with oral secretions
Gram positive diplococci - optochin sensitive, and swells during Quellung reaction
What are the major virulence factors of S. pneumoniae?
Capsule
Pneumolysin - a cytotoxin released when bacteria lyses, inhibits antibody binding to bacteria
Techoic Acid
What are the risk factors for meningitis caused by S. pneumoniae?
immunosuppression (i.e. HIV or recent influenza), distant foci of infection (i.e. chronic otitis media), or low levels of circulating antibodies to capsule
Which H. influenza serotype is responsible for most cases of meningitis? Where does it live?
Hib = Serotype B, with polyribitol phosphate
Asymptomatic carrier in many people’s nasopharynx, but can be spread by aerosol or oral secretions
What is the morphology of H. influenzae and how is it identified?
Gram negative coccobacillus
Identified by needs for factor V (NAD) and factor X (hemin), thus needs to be grown on chocolate agar
What are the meningococcus capsule serotypes causing disease and which one is the most common?
A C B Y W135
like TCBY but ACBY
B causes 50%, and it has sialic acid in it so we couldn’t make a vaccine for it until recently
What are the virulence factors other than capsule for meningococcus and what is its species name?
Pili - for adhesion to epithielum
LOS - lipooligosaccharide, like LPS, same genus as gonorrhea which uses LOS
Neisseria meningitidis
What puts you at risk for Neisseria meningitidis?
Close contact with infected people and areas of outbreak, i.e. college dorms or army barracks
It is the second leading cause of bacterial meningitis
Other than regular meningitis symptoms, what is distinctive about the symptoms of meningococcal meningitis?
Hemorrhagic rash with petechiae, due to the septicemic inflammation from LOS
Petechiae are from disseminated intravascular coagulation (septic shock)
What is the morphology of N. meningitidis and how can it be told apart from gonorrhea?
Gram negative diplococci
Grows fastidiously on Chocolate Agar
Oxidase positive
Told apart by:
Via sugar fermentation MeninGococcal = ferments maltose and glucose
