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Microbiology Unit II > 7 Bacterial Meningitides > Flashcards

7 Bacterial Meningitides Flashcards

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1
Q

What are the two broad categories of CNS infection?

A

Meningitis - inflammation resulting from an infection within the subarachnoid space

Encephalitis - inflammation in the parenchyma

Both can lead to access formation

Toxicity can be systemic due to exotoxin activity

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2
Q

What was the most common cause of bacterial meningitis prior to 1995?

A

Haemophilus influenzae

Responsible for nearly all of cases

Thanks, vaccine! It’s now down to ~2%

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3
Q

Acute meningitis is characterized by …

A

Symptom onset of hours to several days

Etiologic agents include members from all major groups of infectious agents (bacteria, fungi, parasites)

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4
Q

Chronic meningitis is characterized by symptom progression or persistence for …

A

≥ 4 weeks

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5
Q

What organism currently accounts for over half of all bacterial meningitis cases?

A

Streptococcus pneumoniae

Starting to see abx-resistant strep too - boo hiss

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6
Q

What two things have caused a significant decline in the number of cases of meningitis?

A

Vaccination (Hib)

Universal screening of pregnant women for Group B Strep

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7
Q

Community acquired meningitis is usually caused by what three organisms?

A

S pneumoniae
H influenzae
N meningitidis

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8
Q

Hospital acquired meningitis is usually the result of…

A

Iatrogenic procedures (clinician based, ie Foley catheter, dental surgery) or patients with altered immune status

Gram negative rods
S aureus
Other strep and staph strains

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9
Q

Pathogenesis of bacterial meningitis

A

Mucosal colonization —> entry to bloodstream —> penetration of BBB —> release of inflammatory cytokines —> WBC diapedesis into the CSF —> increased permeability of BBB —> exudation of serum

Symptoms: edema, increased intracranial pressure, altered blood flow

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10
Q

3 pathways for gaining access to the CNS

A

Invasion of the bloodstream and seeding of the CNS (most common)

Retrograde neuronal pathway (as with Naegleria)

Direct contiguous spread (from infections, congenital malformations, trauma)

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11
Q

Classic triad of meningitis symptoms

A

Fever

Headache

Neck stiffness

Other presenting Sx include:
Nausea/vomiting
Sleepiness
Confusion
Irritability 
Delirium
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12
Q

Useful blood studies to consider in meningitis patients

A

CBC

Serum electrolytes

Serum glucose (compared to CSF glucose) - will be normal in serum but low in CSF

Liver profile

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13
Q

Additional tests to consider (other than blood tests) for meningitis

A

Cultures (blood, nasopharynx, urine, skin lesions, respiratory secretions)

Lumbar puncture and CSF analysis

Neuroimaging

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14
Q

How do we treat meningitis?

A

Prompt initiation of appropriate empiric therapy (rational therapy after ID of organism and abx susceptibility testing)

Steroid (usually dexamethasone) to decrease swelling

Intrathecal abx for hospital acquired infections (b/c more aggressive)

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15
Q

Predisposing factors for neonatal meningitis

A

Neonatal factors:
Immaturity of host defense mechanisms
Immaturity of organ systems
Low birth weight

Maternal factors:
Premature rupture of membranes
Urogenital infection during late term
Intrauterine infection during early term
Invasion of the uterine space
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16
Q

SSx of meningitis in neonates

A

Bulging fontanelle

High pitched cry

Hypotonia

Paradoxic irritability (quiet when stationary, crying when held)

Hyperthermia** (sometimes hypo)

CNS manifestations (lethargy, irritability, seizures)

GI disturbance (anorexia, vomiting, distention, diarrhea)

Respiratory abnormalities (dyspnea, apnea, cyanosis)

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17
Q

Predominant agents of neonatal meningitis

A

Streptococcus agalactiae

Escherichia coli

Listeria monocytogenes

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18
Q

CDC recommendations for the prevention of neonatal meningitis

A

Universal prenatal screening for vaginal or rectal colonization with group B strep for all pregnant women at 35-37 weeks gestation

Routine abx prophylaxis for culture-positive women (unless undergoing planned cesarean delivery AND who have not begun labor or had rupture of membranes)

19
Q

What is the prognosis for neonatal meningitis?

A

Generally poor (mortality rates of 10-60%)

Survivors typically have permanent defects (ie neuro sequelae)

20
Q

Most common cause of neonatal bacterial meningitis

A

Streptococcus agalactiae (aka Group B Strep)

Not to be confused with Strep pneumo - most common cause of ALL bacterial meningitis

21
Q

Infections of Streptococcus agalactiae in adults is strong linked with…

A

Underlying immunodeficiences

22
Q

What does Strep agalactiae look like?

A

Gram positive coccus

Gray-white colonies with a narrow zone of ß-hemolysis

~80% of cases are transmitted during delivery

Remainder of cases are acquired postpartum

23
Q

What are the virulence factors for Streptococcus agalactiae?

A

Fewer compared to Strep pneumo

Capsular polysaccharide
Hyaluronidase and Collagenase (both help it embed deeper into tissue)
Hemolysin

24
Q

Describe early onset Group B Strep infection

A

Maternal obstetric complications are common

Symptoms develop during first 5 days of life - but has a better prognosis than late onset disease

Major clinical manifestations are bacteremia, PNA, and meningitis

25
Q

Describe late onset Group B Strep infections

A

Maternal obstetric complications uncommon

Symptoms develop from 7 days to 3 months of age (makes Dx more problematic)

Major clinical manifestations are bone/joint infections, bacteremia with concomitant/fulminant meningitis

Poor prognosis

26
Q

What is this stupid CAMP factor test?

A

Developed by Christie, Atkins, and Munch-Peterson

Accentuation of hemolysis due to interaction with staph ß-lysin

Only Strep agalactiae will make this pattern

Horrible test but always on boards 🙄

27
Q

How is Streptococcus agalactiae diagnosed?

A

Organism isolated form normally sterile areas (ie CSF) as well as from areas with mixed flora

CAMP factor

Other presumptive tests:
ID of group CHO is insensitive
DNA probe is available

Definitive Dx requires isolation from blood, CSF

28
Q

Gram-negative enteric bacillus that can be a causative agent for neonatal meningitis

A

E. coli

Encapsulated (K1) strains are associated with meningitis

Source is rectal colonization of mother’s vagina (not an endogenous infection)

Meningitis infections rare in adults but can follow neurosurgical trauma

29
Q

Predisposing conditions for pneumococcal meningitis

A

Multiple myeloma
Sickle cell disease
Cardiorespiratory disease
Congenital defects

30
Q

Non-motile, gram-negative coccobacillus that can potentially cause bacterial meningitis

A

Haemophilus influenzae

Prior URI and associated or preceding otitis media are common

Usual pattern:
Several days of mild antecedent infection followed by deterioration, SSx of meningitis

31
Q

Most causative agents of bacterial meningitis occur during the winter, except …

A

Listeria monocytogenes (occurs in summer)

32
Q

Describe Listeria monocytogenes

A

Gram positive motile coccobacillus

Requires reduced oxygen tension for in vitro growth

Non-fastidious and grows at wide range of temperatures (but does require some CO2)

Numerous serotypes exist but only 3 account for most cases

Facultative intracellular pathogen
• In epithelial cells
• In macrophages and monocytes (shuts down phagocytosis)

33
Q

What are the virulence factors for Listeria monocytogenes

A

LPS-like surface component
• Antiphagocytic
• Presumably responsible for induction of complement-dependent hemolytic antibodies

Listeriolysin O
• Disrupts the phagolysosome membrane
• Inhibits antigen processing
• Induces apoptosis

34
Q

The two main manifestations of listeriosis:

A

Sepsis

Meningitis

35
Q

Clinical manifestations of neonatal listeriosis

A

Acquired in uterine results in stillbirth, abortion, death, or PNA, seizures, skin lesions w/ high mortality if undiagnosed early

Acquired form mom’s genital tract —> meningitis

36
Q

Clinical manifestations of adult listeriosis

A

Leading cause of meningitis in CANCER and RENAL TRANSPLANT patients

Brain stem encephalitis is a classic feature

37
Q

How is listeriosis diagnosed

A

Gram stain of appropriate clinical material
• 60% of meningitis cases are negative
• Organisms are pleomorphic
• Usually grown on blood agar plates

Culture from appropriate clinical material
• Homogenization is required for tissues

38
Q

“Tumbling” motility in a hanging drop preparation is indicative of …

A

Listeriosis

39
Q

Treatment for listeriosis

A

DOC: IV Ampicillin
Alternate: TMP-SMX

40
Q

Describe Neisseria meningitidis

A

Fastidious, gram negative, kidney bean shaped diplococcus

Encapsulated, but only a few serotypes are responsible for disease

41
Q

The most important (disease causing) serotypes of Neisseria meningitidis

A

A, B*, C, Y, W135

All but B are part of the quadrivalent vaccine (B has its own vaccine)

42
Q

Widespread eruption of a rash with petechiae and pink macules within hours is a hallmark sign of …

A

Meningococcal meningitis (from Neisseria meningitidis)

DIC and gram-negative shock can also occur

Can use the “Tumbler test” to determine if it’s the right rash

43
Q

How do you diagnosis meningococcal meningitis?

A

Characteristic petechiae lesions that don’t blanch with pressure

Gram stain CSF

Cultivation of blood on Chocolate agar or Thayer-Martin agar

Detection of capsular polysaccharide in CSF

44
Q

What is the drug of choice for meningococcal meningitis?

A

Penicillin G

Chloramphenicol or 3rd gen cephalosporins are alternatives

Chemoprophylaxis of exposed contacts with various drugs

Microbiology Unit II (7 decks)

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