Morphology and Physiology
Under the microscope, meningococci appear as paired cocci (diplococci) resembling kidney beans or coffee beans, touching at their concave sides. Their size is about 1 µm. They do not retain Gram stain (Gram-negative).
Pili and a microcapsule are located on the surface of the bacterium, capable of transforming into a prominent capsule.
Meningococci require specific conditions for growth: they are aerobes and capnophiles (requiring elevated carbon dioxide levels). Media must contain amino acids; the optimal temperature is 37 °C in a slightly alkaline medium (pH 7.2–7.6). Biochemically, the pathogen has low activity: it breaks down only glucose and maltose with acid production, which is used to differentiate it from other Neisseria species.
Pathogenicity factors
Meningococcal virulence depends on several key structures:
- Endotoxin (lipooligosaccharide): the main aggression factor. Upon bacterial destruction, it enters the bloodstream, causing vascular damage, hemorrhages, and infectious-toxic shock.
- Capsule: protects the bacterium from phagocytosis by phagocytes (antiphagocytic effect).
- Pili and outer membrane proteins: provide attachment (adhesion) to mucosal cells and penetration into them.
- IgA proteases: destroy secretory antibodies, helping evade the immune response.
Epidemiology and infection progression
The only source of infection is humans (sick individuals or carriers). The transmission mechanism is aerogenic (via airborne droplets). The bacterium settles on the nasopharyngeal mucosa.
Disease progression depends on immunity:
- Healthy carriage: the most frequent variant, where the bacterium lives on the mucosa without symptoms (up to 80% during epidemic periods).
- Localized form: meningococcal nasopharyngitis (inflammation of the nasopharynx).
- Generalization: the bacterium breaks through local barriers, enters the bloodstream (meningococcemia), spreads throughout the body, and crosses the blood-brain barrier, causing purulent meningitis.
Diagnostics and prevention
Materials for study include cerebrospinal fluid (CSF), nasopharyngeal secretions, or blood. Diagnostic methods include:
- Bacterioscopy: searching for intra- and extracellular Gram-negative diplococci in the CSF.
- Culture method: inoculation on special media followed by differentiation from non-pathogenic Neisseria.
- PCR and DFA: as rapid diagnostic methods.
- Serology: from the second week of the disease.
Prevention includes patient isolation, ventilation, and avoiding crowding. According to epidemiological indications, a chemical polysaccharide vaccine is used (against serogroups A, C, etc., but it does not protect against group B).
Briefly: answers to topical questions
What nutrient media are used for culturing meningococci?
Special enriched nutrient media are used for culturing meningococci, as they do not grow on simple media. Blood, blood serum, egg yolk, amino acids, and vitamins must be added to the media composition.
Main media used:
- Blood agar (5%) — translucent grayish colonies without a zone of hemolysis are formed.
- Serum agar (including 0.1% semi-fluid) — causes intense turbidity.
- Serum broth — gives homogeneous turbidity.
- Thioglycollate medium.
Which antibiotics are the drugs of choice for treating meningococcal infection?
The drugs of choice for treating meningococcal infection are penicillins (benzylpenicillin, ampicillin). At the pre-hospital stage, if meningococcemia is suspected, emergency parenteral administration of penicillin is indicated.
Alternative systemic antibacterial drugs used include:
- III and IV generation cephalosporins — ceftriaxone, cefotaxime, cefepime.
- Carbapenems — meropenem.
- Fluoroquinolones — ciprofloxacin (prescribed taking regional susceptibility into account).
What clinical forms of generalized meningococcal infection are distinguished?
Several hematogenously generalized forms of meningococcal infection are distinguished.
Main clinical forms:
- Meningococcemia — acute meningococcal sepsis (typical, fulminant, or chronic forms).
- Meningitis — purulent inflammation of the meninges.
- Meningoencephalitis — spread of inflammation to the brain parenchyma.
- Mixed (combined) form — a combination of meningococcemia and meningitis (the most common form).
- Rare forms — endocarditis, myocarditis, pericarditis, arthritis, iridocyclitis, conjunctivitis.
Which main causative agents of purulent meningitis must meningococci be differentiated from?
Sources directly note that the clinical presentation of purulent meningitis can be similar to pneumococcal meningitis; opportunistic flora is also mentioned. A separate list of main pathogens for the differential diagnosis of meningococcus is not provided in the cited sources.
What modern vaccines are used for protection against serogroup B meningococcus?
A specialized recombinant vaccine is used to protect against serogroup B meningococcus, as standard chemical polysaccharide vaccines (groups A and C) are ineffective against it.
Modern preparation:
- Recombinant (rDNA) subunit adsorbed vaccine — intended specifically for the prevention of infection caused by Neisseria meningitidis serogroup B.
Class and exam questions
Why is meningococcal infection accompanied by a hemorrhagic rash?
The rash is caused by the meningococcal endotoxin, which damages the vascular endothelium. This leads to microcirculatory disorders, capillary spasm, and hemorrhages into the skin and internal organs.
Who is the source of infection?
Humans only. "Healthy" carriers pose the greatest danger because they are asymptomatic and actively shed bacteria into the environment.
What is the basis of meningococcal classification?
Based on structural differences in capsular antigens. There are 13 serogroups, with the most clinically significant being A, B, C, X, Y, and W-135.
What else to study on this topic
- Detailed characteristics of the meningococcal antigenic structure
- Mechanisms of DIC syndrome development in meningococcemia
- Characteristics of immunity after a past infection
- Principles of differential diagnosis with opportunistic Neisseria species
- Treatment of meningococcal infection: drugs of choice
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