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Microbiology > Exam #7: Bacterial Infections of the CNS > Flashcards

Exam #7: Bacterial Infections of the CNS Flashcards

1
Q

What are the two categories that CNS infections are divided into?

A

Meningitis= infections of the meninges

Encephalitis= infections of the brain parenchyma itself

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2
Q

What must microbes disrupt to gain access to the CNS?

A

BBB

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3
Q

What is hematogenous spread?

A

Spread through the bloodstream e.g. bacteremia

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4
Q

What are the different modes of entry to the CNS?

A

1) Hematogenous spread
2) Spread from an adjacent site
3) Direct inoculation (rare)
4) Neuronal spread e.g. HSV

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5
Q

What is acute pyogenic meningitis?

A

Bacterial meningitis that leads to the proliferation of neutrophils

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6
Q

What is aseptic meningitis?

A

Viral meningitis (historical term, meningeal inflammation without growth on culture)

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7
Q

How does bacterial meningitis compare to viral meningitis?

A

Bacterial is generally more severe

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8
Q

Who is predisposed to get meningitis?

A

Pneumococcal meningitis:
- Pneumonia & chronic OM

Meningococcal meningitis:

  • 10-20 % population are carriers
  • History of recent UTI–>easier to get into the CNS
  • MAC (terminal) Complement deficiencies
  • Outbreaks are most common in winter

Generally, individuals with altered or underdeveloped immune status are at an increased risk of developing bacterial meningitis

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9
Q

What are the common virulence factors associated with bacterial pathogens that cause CNS infections?

A
  • Capsules= anti-phagocytic

- Fimbriae, pilli, & outer membrane= function in attachment & colonization

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10
Q

Describe the general pathophysiology of meningitis.

A

1) Bacterial penetration of the BBB

2) Inflammatory reaction*
- Many of the clinical manifestations are a result of the immune response in the confined area of the brain

3) Cell wall & toxin components of bacteria exacerbate the inflammatory response
- IL-1 & TNF-a –>ICP, Altered cerebral blood flow, Cerebral edema

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11
Q

What symptoms are characteristic of meningitis?

A

Fever
Headache
Stiff neck (nuchal rigidity)

  • AMS
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12
Q

What CSF abnormalities are associated with bacterial meningitis?

A

*Presence of PMNs
Decreased glucose
Increased protein
Increased pressure

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13
Q

What CSF abnormalities are associated with viral meningitis & encephalitis?

A

Mono/lympho
*Rare PMN
Normal glucose
Normal or slight increased protein & pressure

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14
Q

What is the approach to empirical treatment of suspected CNS infection?

A

1) Empirical abx therapy is generally initiated
2) Age, predisposing factors, and other symptoms may provide clues
3) Examination of CSF & results should direct treatment plan

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15
Q

Who is most commonly infected with bacterial meningitis?

A

Infants & children

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16
Q

What are the MOST common etiological agents that cause bacterial meningitis in children?

A

Listen in order:

S. pneumoniae
N. meningitides 
Group B step. 
Listeria monocytogenes 
Haemophilus influenzae
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17
Q

What is the most common cause of bacterial meningitis in neonates (<1 month)?

A

Group B Strep (S. agalacticae)

Note that this is especially common in kids that are less than 2 months old

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18
Q

What pathogen becomes increasingly prevalent in the teenage years?

A

N. meningitidis

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19
Q

What pathogen becomes more prevalent in the very young & old?

A

Listeria monocytogenes

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20
Q

List the characteristics of S. pneumoniae.

A 
Gram positive coccus
Catalase neg 
Chains
Diplococci 
Oval 
a-hemolytic 
Optochin sensitive

Capsulated

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21
Q

What is the most common cause of vaccine preventable death in the US?

A

Pneumococcal disease

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22
Q

What clinical syndromes may pneumococcal meningitis follow?

A

Pneumonia

OM

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23
Q

List the virulence factors associated with S. pneumoniae.

A

Capsule
Pneumolysin= kills WBC
IgA protease

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24
Q

Describe the course of pneumococcal meningitis infection.

A

Acute onset
High mortality
Neurological sequela

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25
Q

How is pneumococcal meningitis diagnosed?

A

Clinically

  • Gram stain CSF
  • Latex agglutination
  • Standard culture….etc.
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26
Q

How is pneumococcal meningitis treated?

A

Medical emergency, begin empirical abx therapy with vancomycin & a cephalosporin

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27
Q

How is pneumococcal meningitis prevented?

A

Vaccination; however, note that there are 90 different capsular polysaccharides

  • Not ALL are covered
  • However, currently we have a varieties of polysaccharide vaccines
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28
Q

What is PPV23 & what is the problem with PPV23?

A

This is the 23 valent vaccine for S. pneumonia that came out in the 1980s–DOESN’T work well in young kids

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29
Q

What are the current vaccine recommendations for S. pneumoniae

A
  • Recommended for kids >2 with chronic illness, immunosuppression, & other risk factors
  • Also recommended for adults >65
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30
Q

What is PCV13?

A

Pneumococcal polysaccharide conjugated nontoxic diptheria toxin
- 13 serotypes

31
Q

List the characteristics of Neisseria meningitidis.

A 
Gram - diplococcus 
Kidney bean appearance
Oxidase positive 
Catalase positive 
Capsule 
LOS
32
Q

How does LOS differ from LPS?

A
  • Shorter side chains

- No repeating polysaccharide

33
Q

How is Neisseria meningitis cultured?

A

CO2 supplementation

34
Q

What infections does Neisseria meningitis cause?

A 
Meningitis 
Bacteremia 
Pneumonia 
Arthritis 
OM 
Epiglotittis
35
Q

How is Neisseria meningitis transmitted?

A

Aerosolized droplets

36
Q

What are the clinical features of Neisseria meningitis infection? How does meningcococcal meningitis differ from pneumococcal meningitis?

A

Neisseria meningitis presents as:

  • Abrupt onset fever
  • Headache
  • Neck pain
    i. e. as typical meningitis

However, meningococcal meningitits also is accompanied by:

  • Rash
  • hypotension
  • multi-organ failure
37
Q

What causes the rash seen in Neisseria meningitis infection?

A

Antibody complexes

38
Q

How is Neisseria meningitis treated?

A

Vancomycin and/or a cephalosporin followed by once N. meningitidis is identified PCN

39
Q

How is meningococcal meningitis prevented?

A

Vaccination

Serotypes A, C, Y, W-135, BUT NOT B

40
Q

What serotype causes half of the meningococcal meningitis causes in children under 2? Is there a vaccine for this strain?

A
  • Serotype B

- No

41
Q

How is meningococcal meningitis diagnosed?

A
  • Recognize clinical signs & symptoms
  • Gram stain CSF
  • Rapid antigen detection in CSF
42
Q

Describe the current meningococcal vaccine that is used in clinical practice.

A

“MCV4” -Meningococcal Conjugate Vaccine

Tetravalent polysaccharide conjugate vaccine

43
Q

List the characteristics of Streptococcus agalactiae.

A 
Gram + cocci 
Chains
Catalase negative 
B-hemolytic 
Group B
44
Q

What patient population is most susceptible to GBS meningitis?

45
Q

What other infections are caused by GBS?

A

Sepsis
UTI
Soft tissue infections

46
Q

Why is the neonate susceptible to GBS infection?

A
  • 10-30% of pregnant women are colonized by GBS
  • Thus, maternal intrapartum GBS colonization is a MAJOR risk factor for the development of early onset disease in infants

*Note that maternal colonization increases risk of infection x25

47
Q

What virulence factors are associated with GBS?

A

Polysaccharide capsule

48
Q

Aside from maternal GBS colonization, what else increases the risk of GBS meningitis in the neonate?

A
  • Obstetric issue
  • GBS bacteuria
  • Previous infant with GBS infection
  • African American
  • Low GBS antibody
49
Q

What are the characteristics of early onset GBS disease?

A

Early onset= within the first week of life

Disease is characterized by bacteremia, pneumonia, & meningitis

  • Respiratory distress
  • Labored breathing
  • Fever
  • Lethargy
  • Irritability

*Note that 1/4 that survive will suffer from permanent neurological sequela

50
Q

What are the characteristics of late onset GBS disease?

A

Late onset= between 1-3 weeks after birth

Similar signs and symptoms of “early onset,” but meningitis is more common

51
Q

How is GBS diagnosed in the neonate?

A
  • Recognition of clinical signs and the identification of the organisms–FEVER in NEONATE is a BIG DEAL
  • Identification of organism in CSF
  • Serologic confirmation by presence of Group B antigen
52
Q

How is GBS treated?

53
Q

How is neonatal GBS prevented?

A
  • Universal screening of all pregnant women
  • Intrapartum antibiotics i.e. high doses of IV PCN ~4 hours prior to delivery

*Note that there is no vaccine to prevent GBS

54
Q

List the characteristics of Haemophilus influenzae type B.

A

Gram negative rod
Requires X & V
Chocolate agar
Encapsulated

55
Q

What serotype of Haemophilus influenzae causes meningitis?

56
Q

Is there a vaccine for HiB?

A

Yes, (conjugated) vaccine against the poly-ribitol phosphate (PRP) capsule

57
Q

What diseases are caused by non-encapsulated Haemophilus influenzae?

A

Pinkeye
OM
Sinusitis

58
Q

What diseases are caused by encapsulated Haemophilus influenzae?

A

Meningitis

Epiglottitis

59
Q

What is the major neurological sequelae from HiB meningitis?

A

Hearing loss

60
Q

How is HiB diagnosed?

A

Gram stain CSF

Latex agglutination test

61
Q

How is HiB treated?

A

Similar to other forms of bacterial meningitis–broad to narrow spectrum

62
Q

List the characteristics of Clostridium tetani.

A
  • Gram + rod
  • Anaerobic
  • Spore forming–soil & feces
  • Neurotoxin–tetanospasmin
63
Q

Describe the typical entrance mechanism of Clostridium tetani.

A
  • Spores enter through wound contamination or traumatic inoculation
  • Umbilical stump can be contaminated in neonatal tetanus
64
Q

What is tetanospasmin? Describe the mechanism of action.

A
  • AB tetanus toxin
  • B binds to motor neurons via polysaialoganglioside receptors
  • Entire toxin is internalized & retrogradely transported to the spinal cord
  • In the spinal cord, it activates the release of GABA
  • Leads to “SPASTIC PARALYSIS”
65
Q

What are the symptoms of tetanus?

A

Descending pattern of symptoms as follows:

“Lock jaw”
Neck stiffness
Difficulty swallowing
Muscle rigidity

66
Q

How is Tetanus diagnosed?

A

Mostly based on clinical presentation & exposure history

67
Q

How is Tetanus treated?

A

Passive & active immunization

  • Administer Ig
  • Vaccinate with inactivated tetanus toxin
68
Q

How is Tetanus prevented?

A

Vaccination with tetanus toxoid–the “T’ in DTaP

formalin inactivated tetanus toxin

69
Q

List the characteristics of Clostridium botulinum.

A

Gram positive rod
Anaerobic
Spore forming
Produce neurotoxin

70
Q

What is Infant Botulism?

A

“Floppy baby” Sydrome

  • Infants ingest honey containing spores & produce toxin
  • Most common cause of Botulism in the US
71
Q

List the characteristics of Listeria monocytogenes.

A

Gram + rod

Motile

72
Q

What is Listeria monocytogenes associated with?

A

Consumption of contaminated food i.e. deli meat, milk, cheese, poultry

*Transplacental transmission to neonate

73
Q

How does Mycobacterium tuberculosis compare to other bacterial meningitis infections? What diseases can it cause?

A

Chronic symptom onset

  • Meningitis
  • Brain abscess
74
Q

What CNS infections can S. aureus cause?

A

Meningitis

Brain abscess

Microbiology (49 decks)

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