Neisseria meningitidis

Question 1

N. meningitidis

Morphology

Answer 1

Aerobic

Gram Negative

Coffee Bean-shaped Diplococci

With/Without Polysaccharide Capsule

Fastidious: Requires Enriched media @ 35-37 C with CO2

Human-specific

Colonizes Nasopharynx (commensal)

2 Forms of Disease:
1) Can cross Nasopharyngeal Barrier, survive, and replicate in the Bloodstream

2) Can cross BBB to cause Meningitis.

Note: Most serious infections of the Lungs and Meninges are due to Encapsulated Bacteria because the Capsule is Anti-Phagocytic.

Serogroups:
_13 serogroups
_Only 6 serogroups cause life-threatening disease.

Question 2

Collection and Transport of CSF Specimen

Answer 2

Bacterial Meningitis:
_If suspected, CSF is best clinical specimen for isolation, identification, and characterization.
_Collect in Trans-Isolate (T-I) Medium if CSF cannot be analyzed immediately (within 24 hrs).

________________

Algorithm for CSF
(w/o T-I media):

1) Centrifuge CSF sample.

2) Do Latex Agglutination of Supernatant:
_Looking for Soluble Polysaccharide Capsule.

3) Gram Stain the Sediment

4) Or can Plate the Sediment on
Chocolate Agar and Blood Agar.

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Algorithm for CSF with T-I Medium:

1) Inoculate Trans-Isolate medium
2) Incubate Overnight 35 C in CO2
3) Culture on Chocolate Agar and Blood Agar.

Question 3

Collection and Transport of Blood Specimen

Answer 3

Why Take Blood Specimen:

1) If a Spinal Tap is Contraindicated.
2) When Bacteremia is Suspected.

Steps:

1) Culture in Trypticase Soy Broth (TSB)
or Brain Heart Infusion Broth (BHI).

2) Neutralize with chemical inhibitors any normal bactericidal properties of blood (e.g. patient’s antibodies in the sample as immune response) and any potential antimicrobial agents.
3) Incubate Overnight
4) Culture

Question 4

Culture

Answer 4

Blood Agar Plate (BAP):

1) Trypticase Soy Agar + Sheep Blood
2) Plate should appear Bright Red.

3) Uses: N. meningitidis and Streptococcus pneumoniae
________________

Colonies on BAP:

1) Unpigmented, Smooth, Glistening
2) Appear Round with a Clearly Defined Edge

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Chocolate Agar Plate (CAP):

1) Supports special growth requirements (Hemin and NAD) for the Isolation of Fastidious microbes.
2) Can be prepared with Heat-Lysed Horse Blood (Good Source of both Hemin and NAD) or Sheep Blood.
3) NAD is Released from the Blood during the Heating Process
4) Hemin is available from Non-Hemolyzed and Hemolyzed Blood cells.

Changes from red to brown color (chocolate) due to heat-lysing of blood.
________________

Colonies on CAP:
1) Large

2) Colorless-to-Grey, Opaque

Question 5

Identification of Neisseria meningitidis

Answer 5

1) Kovac’s Oxidase Test Positive:
_Oxidase Reagent is turned into a Purple compound by **Cytochrome Oxidase C
_Cytochrome Oxidase C is located in the Inner Plasma Membrane of Aerobic Bacteria.
_Identification test for Neisseria species.

2) CTA Sugar Reactions for N. meningitidis:
_Utilization of *Glucose (Dextrose) and *Maltose, indicated by Acid Production (Color Change to Yellow)
_and No Utilization of *Lactose
_Specific for N. meningitidis

3) Serology: Slide Agglutination Serogrouping Test for N. meningitidis (SASG):
_Antibodies for specific serogroups are added to different slides.
_The Antibodies bind to the Bacterial cells, causing the cells to Agglutinate (clump), making the cell suspension appear clearer.
_Positive Result: Strong agglutination within 1-2 minutes.

4) Molecular Tests (PCR):
_Genetic maps of specific protein genes for specific Serogroups.
_Tells the Serogroup.

Question 6

Transmission and Carriage

Answer 6

Transmission:

1) Respiratory Secretions or Saliva in very close contact
2) Leading to Colonization of Nasopharynx
3) Or Leads to Invasive Disease

May spread from Nasopharynx to Adjacent epithelial surfaces and infrequently can cause Local infections:

1) Pneumonia
2) Sinusitis
3) Otitis Media

Meningococcal Disease usually occurs within 1-14 Days after Acquisition.

Carriage immunizes person, providing protective immunity against it.

Carriage is Highest in Older Children and Young Adults.

1) Highest in Adolescents
2) Increases in Closed Populations

Meningococcal Carriage is Affected by
_Age
_Intimate personal contact
_Crowding (Bars, Dormitories)
_Smoking
_Very Low Humidity
_Drying of Mucosal Surface

Question 7

Host Susceptibility

Answer 7

**Absence of Protective Antibodies:
_The most important single predisposing factor for Systemic Meningococcal Disease

_Lose Maternal Antibodies after ~6 months; baby is supposed acquire its own antibodies then.
_Increased risk for infants and young children
_Congenital or Acquired Antibody Deficiencies.

Genetic Polymorphisms and other Host co-factors.

Question 8

Virulence Determinants

Answer 8

The Major Outer Membrane Components:

1) Polysaccharide CAPSULE:
_Prevents Phagocytosis
_or Prevents Complement-mediated Lysis

2) LipoOligosaccharide (LOS), Endotoxins:
_Crucial in Inflammatory Signaling

3) Type IV Pili:
_Attachment!!

Question 9

Meningococcal Meningitis

Answer 9

Sudden Onset:

1) Fever
2) Headache
3) Stiff Neck

Accompanied by

4) Nausea
5) Vomiting
6) Photophobia
7) Altered Mental Status

Low Concentration of Meningococci and Endotoxin in Plasma

High Concentrations in CSF

Overall inflammatory response (cytokines and complement activation) in the systemic vasculature is modest.

Question 10

Meningococcemia

Answer 10

Bacteremia by N. meningitidis is far more severe than its Meningitis.
_May present with Mild symptoms, then Rapidly Deteriorate within 24 hours.

1) Rapid Proliferation of Meningococci in Circulation.

2) Severe, Persistent Shock
_Lasting More than 24 hrs or until Death

Large Bacterial Growth Causes Exaggerated and Destructive

3) Intravascular Inflammatory Response, leading to
4) Progressive Circulatory Collapse, and to
5) Severe Coagulopathy

6) Develop Impaired Renal, Adrenal, and Pulmonary Function,
7) And develop Disseminated Intravascular Coagulation with Thrombotic Lesions.

Note: All of the above are common in Severe Gram Negative infections.

8) Vascular Complications:
_Can lead to Loss of Digits or Limbs
_Survivors can be Severely Handicapped

9) Usually Admitted because of Fever and Rash (Petechial or Purpuric)

10) No Distinct Clinical signs of Meningitis.
_Few Meningococci in CSF

11) If Untreated, can develop Meningitis or Shock.

Question 11

Treatment

Answer 11

Clinical presentation of Meningococcal Meningitis is similar to other forms of Bacterial Meningitis.

1) Start Empiric Therapy with Broad-Spectrum Antibiotics after appropriate cultures have been obtained:
_3rd Generation Cephalosporin
(Cross BBB well)

2) Few Penicillin-Resistant Strains of Meningococcus reported in U.S..
_Once N. meningitidis infection is confirmed, treatment with Penicillin alone is recommended.

Question 12

Vaccines

Answer 12

Serogroup B (sialic acid):
_Poorly Immunogenic
_Vaccines have limited effect
(Princeton outbreak)

Quadrivalent conjugate vaccine for certain serotypes recommended for young adults (military recruits and college students; adolescents).

Vaccine doesn’t have sustained effect on nasopharyngeal carriage, so “Herd Immunity” does not develop:
_Herd immunity means if vaccine is given to enough people, the vaccine will spread even to those people who were not given the vaccine.