Meningococcus

Menigococcus (Meningococcus intracellularis, s. Diplococcus intracellularis meningitidis Weichselbaum, s. Neisseria intracellularis), the causative agent of epidemic cerebrospinal meningitis. It represents a paired coccus of two individuals facing each other with flattened surfaces (resembling a coffee bean) [see separate table (p. 743-744), fig. 4]. The cocci may also be located singly or in groups of four individuals. In cerebrospinal fluid, M. is most often found inside cells; however, this intracellular position is not the rule. M. is characterized by great diversity in size and shape; along with small ones, very large cocci are also encountered, several times exceeding the usual size. It is decolorized by Gram's method. The stainability of M. in postmortem material may decrease significantly. M. is a strict aerobe; when freshly isolated, it grows only on media containing ascitic or serous pleural fluid or blood serum. In subsequent generations, it also grows on ordinary nutrient media without the addition of ascitic fluid or serum. Of sugars, it decomposes glucose and maltose, with the medium acquiring an acidic reaction; it has no effect on other sugars. On ascitic agar (best in a ratio of 1:3), the growth is characteristic: after 20 hours, colonies 1-3 mm in diameter appear, round, grayish, translucent, with a dull luster; they are easily removed and readily emulsified. After 48 hours, the colonies reach 4-5 mm in diameter, their center is dark with a brownish tint. A beneficial improvement to the medium is the addition of grape sugar (1-2%) to ascitic agar. Many special media have been proposed for growing M.; worthy of mention is agar with human blood (Schottmüller's) and with grape sugar (Zeissler's), prepared by adding 20% sterile human blood and 2% grape sugar to meat-peptone agar. The medium has differential-diagnostic significance: colonies of M. are round, 1-6 mm in diameter, flat, grayish in color with a violet tint. M. belongs to the group of very low-resistant microorganisms; when heated in a liquid medium to 100°, it dies instantly; at 70°, it dies in 5 minutes; according to Dopter, most of the culture already dies at 41°. M. is extremely sensitive to drying. In the absence of special protective measures against drying, M. cultures on ascitic agar may die in just 2-3 days. M. is also very sensitive to the action of disinfectants; a 1% solution of lysol, carbolic acid, or creolin kills M. in 1 minute; the same effect is produced by a 1:1000 solution of sublimate. Direct sunlight kills M. in 4-6 hours (Dopter), while scattered light leaves them alive even after 5-6 days of exposure. It is not possible to cause cerebrospinal meningitis in experimental animals using M.; the exception is only certain species of monkeys, and for this, large quantities of M. must be introduced directly into the spinal canal or subdurally. Recently, P. F. Zdrodovsky succeeded in causing experimental meningitis in rabbits by introducing meningococci via suboccipital puncture. There are several types of M. Dopter first drew attention to this in 1909, when he isolated diplococci from nasopharyngeal mucus that were morphologically, biologically, and in terms of growth completely similar to M., but did not agglutinate with immune antimeningococcal serum. Dopter called them parameningococci and then divided them into subgroups α, β, and γ. Gordon and Murray (1911), using the agglutination reaction and the method of specific adsorption of agglutinins, divided M. into 4 types: I, II, III, and IV, with I and III on one hand, and II and IV on the other, being close to each other. In France, Nicolle, Debain, and Jouan, abandoning Dopter's classification, established the existence of 4 types of M., naming them A, B, C, and D. Type A corresponds to types I and III of Gordon; type B to types II and IV, whereas types corresponding to the French C and D do not exist in the English classification. In Denmark, in addition to the four Gordon types, Thomsen and Wulif also isolated type A, which stands apart. In the USSR, Chel'ny studied 43 M. cultures, with type A found 19 times and type B 21 times, while the other three cultures did not agglutinate with any of the four types of serum. During 1924-26, Trotsky isolated 49 M. strains, with 19 strains (39%) corresponding to type A of the French classification, 28 (57%) to type B, and 2 (4%) to type C (the data of Chel'ny and Trotsky concern Moscow and the Moscow region). In general, it is necessary to accept the multiplicity of serologically different types of M., with the types differing from each other in their antigenic properties—a circumstance that is important for both bacteriological diagnosis and treatment (the use of serum corresponding to the type of M. that caused the given disease).- For the diagnosis of epidemic cerebrospinal meningitis, it is necessary to isolate a strain of M. and identify it; the latter is done by means of agglutination with specific serum, and it is necessary to use serum of all 4 types. The diagnostic value of the Widal reaction, as well as the complement deviation reaction, is very limited; these reactions give unreliable results; in particular, determining the type by means of the complement deviation reaction is impossible. From an epidemiological point of view, the fact of the widespread carriage of M. by healthy people in the nasopharyngeal mucus is of great importance (see Meningitis, epidemic cerebrospinal meningitis).