Neisseria meningitidis Flashcards
N. meningitidis
Morphology
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.
Collection and Transport of CSF Specimen
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).
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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.
Collection and Transport of Blood Specimen
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
Culture
Blood Agar Plate (BAP):
1) Trypticase Soy Agar + Sheep Blood
2) Plate should appear Bright Red.
3) Uses: N. meningitidis and Streptococcus pneumoniae
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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.
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Colonies on CAP:
1) Large
2) Colorless-to-Grey, Opaque
Identification of Neisseria meningitidis
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.
Transmission and Carriage
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
Host Susceptibility
**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.
Virulence Determinants
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!!
Meningococcal Meningitis
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.
Meningococcemia
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.
Treatment
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.
Vaccines
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.