The meningococcus
In microbiology, meningococcus is known as Neisseria meningitidis : as shown by the scientific name of the bacterium, meningococcus is the etiopathological agent responsible for meningitis, a rare but very serious disease.
It should be pointed out, however, that meningococcus, despite being a commensal of the oro-pharyngeal tract, can favor particularly severe clinical conditions, which can seriously endanger the life of the affected patient. Meningococcal meningitis continues to remain a medical problem as much felt as feared, especially in developing countries, where the hygienic conditions of the environments and the population are rather scarce; meningococcus, therefore, continues to claim numerous victims and, although the infection has been thoroughly studied by researchers, it has not yet reached an effectively valid pharmacological cure.
Microbiological analysis
Identified only in 1884, meningococcus is a gram-negative obligate aerobic bacterium, immobile, asporiginal, oxidase-positive, having an estimated size of around 0.6 x 0.8 micron; meningococcus can live in pairs (diplococcus) or remain single, and most forms are sensitive to the external environment and to drying. Because of their sensitivity to physical, chemical and mechanical agents, meningococci are often destined for autolysis: the microorganism's autolytic process is an expression of the intervention of some enzymes, whose action is almost comparable to the autolysis of the gonococcus, due to the amidase (enzyme that exerts its action at the level of the gonococcal peptidoglycan).
Furthermore, meningococcus is not able to ferment lactose, rather it ferments glucose and maltose (without creating gas).
The optimal growth conditions for meningococci are:
- 5-10% carbon monoxide atmosphere
- Optimum growth temperature: 35-37 ° C
- Ideal growing medium: chocolate agar
Classification
Being gram-negative bacteria, meningococci have:
- external cell membrane;
- polysaccharide capsule → located outside the cell membrane, the capsule is useful for protecting the bacterium during the infectious process;
- pili → are formed by protein polymers, directly located on the bacterial surface; allow adherence to target cells.
The classification of meningococci must be carried out on the basis of the characteristics of the polysaccharide capsule: starting from the capsular antigens, in fact, these bacteria can be classified into 13 classes (serum-groups), distinguished individually by a letter of the alphabet; among these, the pathogens inserted in class B and C constitute the most widespread serum groups.
The classification of meningococci, however, should not be made exclusively based on the characteristics of the capsule; in fact, a further division of the types of meningococcus was elaborated as a function of the characteristics of the outer membrane proteins and of the lipo-oligosaccharides (antigens of the cell wall or, more simply, LOS), which allowed to differentiate meningococci into types, serotypes and immunotypes .
Causes and incidence
Meningococcus, having a marked tropism (affinity) for the central nervous system, diffuses into the bloodstream starting from the nose-pharynx, and from here it can damage meninges, synovium, skin and adrenal glands.
Meningococcal infections - where the incidence is higher in the so - called meningitis fascia, in Africa - can occur both in endemic and sporadic form (incidence: 10-25 cases per 100, 000 people); in industrialized countries, on the other hand, meningococcal infections are rather rare and are approximately approximately 1-3 cases per 100, 000 inhabitants.
It is observed that the infections mediated by meningococcus tend to affect children aged between 6 months and 5 years, and boys between 15 and 25 years (especially if forced to live in overcrowded environments, such as prisons, barracks, etc.). ). Medical statistics show that most of the meningococcal infections are diagnosed in the winter-spring months, following contact with droplets of saliva emitted by a healthy carrier.
In spite of the great interest of the medical class towards meningococcus, the mechanism by which the bacterium infests the bloodstream is not fully understood; what is shown is that meningococcus, by adhering to human target cells (epithelial cells of the mucosa of the nose-pharynx) by means of pili, begins a process of endocytosis.
A healthy organism, at the first attack by meningococcus, reacts with a specific immune response, producing bactericidal antibodies that, by activating the complement and other cytotoxic mediators, is able to remove and kill meningococcus. According to these words, we understand how a possible alteration of the complement system and / or a deficiency of IgA and IgM antibodies exaggeratedly increases the risk of spreading meningococcus in the bloodstream.
Smoking and passive smoking are two important elements of risk for contracting meningococcal infection: smoking, in fact, damaging the epithelium of the nose-pharynx favors the translocation of the bacillus.
The healthy carrier man is the only natural reservoir of meningococcal infection.
