What is the causative agent of meningococcal infection?

Most meningococci exist in neutrophils. These bacteria are also found in the nasal cavity of most friends, but they basically will not cause disease. Only a very small number of friends will develop nasopharyngeal inflammation. The pathogenic substances of meningococci are generally fimbriae, endotoxins, etc. Meningococci can also cause great harm to the human body and cause diseases such as bacteremia.

Meningococcus, a Gram-negative diplococcus, is mostly located in neutrophils in the cerebrospinal fluid of patients in the acute phase or early stage, forming a double arrangement in a kidney shape with concave surfaces facing each other. Under an electron microscope, it can be observed that the toxic strains isolated from patients have microcapsules and pili. The culture conditions are relatively high. It will not grow on ordinary culture media, but can grow on culture media containing serum or blood, such as heated (above 80°C) blood agar medium (called chocolate blood medium). This bacterium is an obligate aerobe, but when initially cultured, it grows most vigorously in a low-oxygen environment of 5-10% CO2, with an optimum pH of 7.0-7.4 and an optimum temperature of 37°C. After 24-72 hours of culture, the colonies become round, smooth, moist, transparent, and slightly gray-blue. Grows uniformly in serum broth.

Culture conditions/meningococci

The culture conditions are relatively high. It will not grow on ordinary culture media, but can grow on culture media containing serum or blood, such as heated (above 80°C) blood agar medium (called chocolate blood medium). This bacterium is an obligate aerobe, but when initially cultured, it grows most vigorously in a low-oxygen environment of 5-10% CO2, with an optimum pH of 7.0-7.4 and an optimum temperature of 37°C. After 24-72 hours of culture, the colonies become round, smooth, moist, transparent, and slightly gray-blue. Grows uniformly in serum broth.

Resistance/Meningococcal

Meningococci have weak resistance and are sensitive to cold, sunlight, heat, dryness, ultraviolet rays and general disinfectants. It is sensitive to sulfonamides, penicillin, streptotoxin and chloramphenicol, but is prone to develop drug resistance. Based on the differences in the meningococcal surface capsular polysaccharide antigens, the bacteria are divided into nine serogroups: A, B, C, D, X, Y, 29E and W135. Most of the pathogens in humans belong to groups A, B and C. More than 95% of the cases in my country are group A, and groups B and C have been found in some areas. x, y, z, etc. are often found among carriers but rarely cause disease. Each serogroup can be divided into several serotypes based on the outer membrane protein antigen (type specificity).

Pathogenic agent/meningococcus

The main pathogenic substances of meningococci are capsule, fimbriae and endotoxin. Meningococci usually reside in the nasopharynx of normal people. About 5-10% of healthy people carry this bacteria in their nasopharynx, and the rate can be as high as 20-70% during the epidemic period. However, 90% of carriers do not get sick. A few develop nasopharyngitis, and severe cases cause bacteremia. Only 1-2% of people reach the spinal meninges through the bloodstream or lymph and cause purulent meningitis. Carriers and patients are sources of infection. Meningococcal infection is transmitted through droplets and can also be transmitted through contact with objects contaminated by the patient's respiratory secretions. The incubation period is about 1 to 4 days.

The occurrence of this disease is closely related to the body's immunity. When the body's resistance is low, the bacteria that invade the nasopharyngeal cavity multiply in large numbers and invade the bloodstream, causing bacteremia and sepsis. The patient will experience chills, fever, nausea, vomiting, and hemorrhagic rash on the skin. The bacteria can be found in the rash. In severe cases, the cerebrospinal meninges may be invaded, resulting in purulent cerebrospinal meningitis, with symptoms of meningeal irritation such as headache, projectile vomiting, and stiff neck. Even adrenal failure and toxic shock may occur due to bleeding in both adrenal glands.

The occurrence of the above symptoms is related to the release of large amounts of endotoxins due to bacterial autolysis and death. Neisseria meningitidis and gonococci can produce an extracellular enzyme, namely lga protease, which can specifically cleave human lga1 and thus destroy the normal immune function of humans. Its role in pathogenicity is increasingly valued.