Neisseria meningitidis (meningococcus)
For cultivation of pathogenic Neisseria spp. are used special media for cultivation and isolation of nutritionally fastidious microorganisms. If this media contain intact erythrocytes (sheep or horse), Neisseria meningitidis grows on them without hemolysis. As Neisseria meningitidis is resistant to vancomycin and colistin, these antibiotics are often added directly in the medium to inhibit other gram-positive and gram-negative bacteria. Meningococcus require an aerobic atmosphere for its growth. Carbon dioxide enhances growth, but is not required. N.meningitidis is oxidase positive.
Neisseria meningitidis is a heterotrophic gram-negative diplococcal bacterium best known for its role in meningitis and other forms of meningococcal disease such as meningococcemia. N. meningitidis is a major cause of morbidity and mortality in childhood in industrialized countries and is responsible for epidemics in Africa and in Asia. Approximately 2500 to 3500 cases of N. meningitidis infection occur annually in the United States, with a case rate of about 1 in 100,000. Children younger than 5 years are at greatest risk, followed by teenagers of high school age. Rates in sub-Saharan Africa can be as high as 1 in 1000 to 1 in 100. Meningococci only infect humans and have never been isolated from animals because the bacterium cannot get iron other than from human sources (transferrin and lactoferrin). It exists as normal flora in the nasopharynx of up to 5-15% of adults. It causes the only form of bacterial meningitis known to occur epidemically.
Meningococcus is spread through the exchange of saliva and other respiratory secretions during activities like coughing, kissing, and chewing on toys. Though it initially produces general symptoms like fatigue, it can rapidly progress from fever, headache and neck stiffness to coma and death. The symptoms are easily confused with those of meningitis due to other organisms such as Haemophilus influenzae and Streptococcus pneumoniae. Death occurs in approximately 10% of cases. Those with impaired immunity may be at particular risk of meningococcus (e.g. those with nephrotic syndrome or splenectomy; vaccines are given in cases of removed or non-functioning spleens).
Septicaemia caused by Neisseria meningitidis has received much less public attention than meningococcal meningitis even though septicaemia has been linked to infant deaths. Meningococcal septicaemia typically causes a purpuric rash that does not lose its colour when pressed with a glass ("non-blanching") and does not cause the classical symptoms of meningitis. This means the condition may be ignored by those not aware of the significance of the rash. Septicaemia carries an approximate 50% mortality rate over a few hours from initial onset. Note that not all cases of a purpura-like rash are due to meningococcal septicaemia; however, other possible causes need prompt investigation as well (e.g. ITP a platelet disorder or Henoch-Schönlein purpura). Other severe complications include Waterhouse-Friderichsen syndrome (a massive, usually bilateral, hemorrhage into the adrenal glands caused by fulminant meningococcemia), adrenal insufficiency, and disseminated intravascular coagulation.
The gold standard of diagnosis is isolation of N. meningitidis from sterile body fluid. A CSF specimen is sent to the laboratory immediately for identification of the organism. Diagnosis relies on culturing the organism on a chocolate agar plate or a blood agar plate enriched with a growth supplement. Further testing to differentiate the species includes testing for oxidase (all Neisseria spp. show a positive reaction) and the carbohydrates maltose, sucrose, and glucose test in which N. meningitidis will utilize glucose and maltose. Serology determines the group of the isolated organism. Clinical tests that are used currently for the diagnosis of meningococcal disease take between 2 and 48 hours and often rely on the culturing of bacteria from either blood or cerebrospinal fluid (CSF) samples. However, polymerase chain reaction tests can be used to identify the organism even after antibiotics have begun to reduce the infection. As the disease has a fatality risk approaching 15% within 12 hours of infection, it is crucial to initiate testing as quickly as possible but not to wait for the results before initiating antibiotic therapy.
Neisseria meningitidis basic characteristics
- GRAM-NEGATIVE DIPLOCOCCI
- CATALASE: POSITIVE
- OXIDASE: POSITIVE
Identification of Neisseria meningitidis
- Growth on blood agar
- Acid production from glucose
- Acid production from maltose
- No acid production from lactose
- No acid production from sucrose
- ONPG negative
Antibiotic treatment of Neisseria meningitidis
Neisseria meningitidis on agar plates
Neisseria meningitidis tests for identification
Neisseria meningitidis Gram stain
CENTERS FOR DISEASE CONTROL AND PREVENTION (CDC)
- Characteristics of Neisseria meningitidis; CDC
-  Identification and Characterization of Neisseria meningitidis; CDC
- Primary Culture and Presumptive Identification of Neisseria meningitidis, Streptococcus pneumoniae, and Haemophilus influenzae; CDC
- Antimicrobial Susceptibility Testing of Neisseria meningitidis
- PCR for Detection and Characterization of Bacterial Meningitis Pathogens
- Meningococcal Disease
- Bacterial Meningitis