Saviola: Bacterial and Viral infections of the CNS Flashcards
What are normal protein and glucose concentrations plasma? CSF?
Plasma:
protein: 6000
glucose: 100
CSF:
protein: <45
glucose: 2/3 blood glucose (about 60)
What is meningitis?
inflammation of the meninges of the brain or spinal cord, infection located within the subarachnoid space; CSF
What is encephalitis?
inflammation of the brain tissue
what is myelitis?
inflammation of the spinal cord
How can antibiotic therapy potentially exacerbate symptoms of meningitis?
may exacerbate symptoms by lysing cells and releasing immunogenic cell wall components and allowing more vigorous immune response. The worsening symptoms are likely from an increased immune response and inflammation
corticosteroids can be given with antibiotics to decrease the immune response
When is it likely that antibiotics will cross the BBB and kill bacteria?
early in therapy when the BBB is breached due to inflammation
What is a normal immune response of the CNS? How is this different from an infected CNS?
normal: low [Ab], small numbers of lymphocytes, no plasma or polymorphonuclear leukocytes and no complement components found in the CNS
infected:
w/inflammation, BBB is breached at microvascular endothelium. secretion of cytokines from local macrophages into the subarachnoid space–> breack in NNN. serum proteins into CSF, polymorphonuclear leukocytes present. Ab production by plasma cells may occur at site and CMI cells present. Antibiotics can also cross this BBB
What are some routes of infection of the CNS? (8)
- Hemtogenous (blood borne) spread with most infectious agents. From extracranial foci or by retrograde propagation of infected thrombi within emissary veins.
- Neurotropic spread in the case of some viruses
- Spread of organisms through bone
- Injury- traumatic inoculation of extradural bacteria.
- Surgery- shunts etc.
- Congenital problems
- Otitis- by extension.
- Sinusitis- by extension.
What are some symptoms of acute bacterial meningitis? What will the CSF gram stain and bacterial culture show?
fever, headache irritability, stiff neck, convulsions, drowsiness, coma
CSF gram stain and/or bacterial culture usually positive, unless the patient has been treated with antibiotics prior to evaluation.
What is the most common way that organisms enter the subarachnoid space?
blood borne –> crossing the vascular endothelium or the choroid plexus
usually after nasopharyngeal colonization
What is the pathogenesis of acute bacterial meningitis?
organism enters subarachnoid space
organisms multiply
cell wall components accumulate in the CSF and are inflammatory
Migration of neutrophils
Loosening of the BBB results in inflow of fluids and proteins and antibiotics
Cerebral edema as a result of release of toxic factors
Obstruction of flow of CSF back to blood.
Increased ICP.
What are some characteristics of H. influenzae?
gram negative, pleomorphic bacilli.
polysaccharide capsule (type B)=more invasive (we have vaccine for most common invasive/encapsulated types)–>antiphagocytic
requires X and V factors if grown on blood agar, chocolate agar releases X and V factor
respiratory transmission
Nasopharyngeal carriers common of non type b, but not associated with a high incidence of meningitis
What is the most common cause of meningitis in adults and children under the age of 5?
S. pneumoniae (smokers over 65 yo are predisposed)
What are some characteristics of S. pneumoniae?
Gram + lancet shaped diplococcus, a- hemolytic, optichin positive (optichin inhibits its growth)
antiphagocytic capsule
transported across microvasular endothelial cells in a receptor dependent manner.
Meningitis may be a complication of bacteremia, pneumonia, mastoiditis, endocarditis, and sinusitis.
Associated w/ meningitis after a head wound.
pili help adhere to the oropharynx
What are some characteristics of Neisseria meningitidis?
Gram- diplococcus, oxidase positive (cytochrome C), ferments maltose and dextrose (glucose).
Respiratory transmission.
Virulence associated with antiphagocytic capsule, invasive disease- 13 serotypes. Vaccine against A, C, Y, and W-135.
Causes disease mainly in children and young adults.
LOS (Lipooligosaccharide) = important pathogenic factor.
Some strains coat themselves in HOST sialic acid that are attached to galactose residues on LOS and prevents complement induced killing and survive in the blood.
grown on blood agar or chocolate agar plates
Thayer-martin selective agar to isolate from throat
What are some characteristic of Listeria monocytogenes? Who is most likely affected by this?
gram + rod
Motile (tumble at 22C) (actin rockets)
catalase +
food-borne (lunch meat)
**can cause fetal death and and maternal death in pregnant women. also can affect immunocompromised pts
What are some characteristics of S. agalactiae? (where found? who is normally infected and how to prevent it?)
Group B Streptococcus (GBS).
Found in vagina of some women.
Common cause of meningitis, pneumonia, sepsis in newborns
Untreated carriers have 1 in 200 chance of delivering an infected baby.
Preventable- screen for bacteria; intrapartum antibiotics (to the mother).
When are aerobic gram - bacilli likely to cause acute bacterial meningitis?
predisposing conditions= head trauma, neurosurgical procedures, neonates, elderly, immunocompromised
What are some predisposing factors of staphylococci infections in the brain (S. aureus and S. epidermis)?
postneurosurgical, CSF shunts, head trauma, sinusitis, pneumonia.
What is chronic meningitis? What can cause it?
Neurological symptoms and signs persist or progress clinically, and the CSF remains abnormal for at least 4 weeks (replicates slowly)
More rare than acute meningitis.
M. tuberculosis, Brucellosis, Syphilis, Lyme disease.
What is a brain abscess?
focal intrcranial infection in the brain;
Develops into a collection of pus surrounded by capsule
likely Spread from contiguous source- otitis media, mastoiditis, sinusitis, dental trauma, penetrating trauma.
