534 NEISSERIA 



will occur are comparatively narrow, but they depend largely on the constitution 

 of the medium. The optimum temperature for all the members is 37° C. ; some 

 of them,' including the meningococcus and the gonococcus, will not grow at all 

 below 30° C. ; many of the nasopharyngeal cocci will grow at 22° C, but not 

 always on first isolation. The meningococcus forms a weak hsemolysin, reaching 

 its maximum in trypagar cultures in about 4 days. 



Some of the members — the pharyngis flava group — produce a greenish-yellow 

 pigment on solid media, and occasionally a Gram-negative coccus is met with 

 that forms a bright yellow pigment. Some of the Gram-negative cocci, particularly 

 the gonococcus and the meningococcus, contain an active autolysin, which is 

 destroyed by heating to 65° C. for half an hour. 



Cultural Characteristics. — The colonial appearances ot all the Gram-negative 

 cocci appear to be subject to considerable variation. Two different types of colony 

 of both the meningococcus and the gonococcus have been described (Wassermann 

 1898, Lipschiitz 1904, Atkin 1923, 1925, Cohn 1923) ; and S. P. Wilson (1928) 

 and G. S. Wilson and Smith (1928) have observed and studied rough and smooth 

 types of numerous nasopharyngeal cocci. In fluid media — broth and serum broth 

 — growth is generally poor, and takes the form of a slight turbidity and a finely 

 granular deposit, which disintegrates hardly at all on shaking ; occasionally growth 

 occurs on the surface. 



Resistance. — The resistance of the Gram-negative cocci to inimical agencies is 

 very low. In culture most of them die out in a few days ; though if the organisms 

 are seeded into ascitic agar stab tubes — preferably made up with 0-75 per cent, 

 agar — prevented from drying, and kept in the incubator at 37° C, they may live 

 for weeks or even months. Though it is not known with certainty why the Gram- 

 negative cocci die out in culture so quickly, it appears probable that they are killed 

 by the amount of alkali produced ; the production of NH3 and of alkaline car- 

 bonates of organic acids may apparently lower the H-ion concentration of the 

 medium to pH 8-6-90, and thus bring about the death of the organisms (Phelon 

 et al. 1927). The meningococcus and the gonococcus are killed by heating to 55° C. 

 in 5 minutes or less ; they are very susceptible to desiccation, death occurring 

 usually within an hour or two. Weak disinfectants, such as 1 per cent, phenol 

 or 0-1 per cent. HgClg, prove fatal in 1 or 2 minutes. The meningococcus and 

 the gonococcus are both sensitive to the sulphonamides and to penicillin. 



Biochemical Reactions. — Biochemically the members of the group are not very 

 active ; the production of acid in glucose, maltose, and sucrose is used as a means 

 of classification. Other sugars, such as galactose, laevulose, and dextrin, are used 

 by some workers, but those who have had most experience agree that they are 

 unsatisfactory. Since many species of Neisseria will not grow on the ordinary 

 peptone water sugar medium, it is necessary in testing their sugar reactions to add 

 a small amount of serum, or to grow them on ascitic fluid agar containing litmus 

 and 1 per cent, of the sugar. If serum is used, human or rabbit serum should 

 be chosen, since horse, sheep and ox serum contain maltase, which may lead to 

 a false reaction in the presence of maltose (Rosher 1936, Hendry 1938). Litmus 

 milk is unaltered, except by the Diplococcus crassus, which turns it acid. Indole 

 is not produced. The methyl-red test is weakly positive or frankly negative, 

 according to whether or not the organism tested produces acid from glucose ; as 

 the increase in H-ion concentration is rarely greater than to pH 6-0, the red colour 



