536 NEISSERIA 



Classification 



The Gram-negative cocci, as a group, have been studied so little that it is 

 impossible to lay down any satisfactory basis for classification. Apart from the 

 meningococcus and the gonococcus, the definition of the different species is far 

 from clear. This is due largely to the fact that the colonial appearances are sub- 

 ject to such great variation that the descriptions given of apparently the same 

 species by different workers are often quite contradictory. The cultural descrip- 

 tions, for example, of N. catarrhalis are most varied (Ghon and Pfeifier 1902, 

 Dunn and Gordon, M. H., 1905, von Lingelsheim 1906, Arkwright 1907, Gurd 

 1908, Elser and Huntoon 1909, Martin 1911, Netter and Debre 1911, Dopter 

 1921, Gordon, J. E., 1921), and the only sound basis for identification of this 

 organism appears to be its failure to ferment any sugars. Again, in Germany 

 and America, several chromogenic species have been described, forming a greenish- 

 yellow pigment, producing acid in glucose, maltose, and sometimes sucrose, and 

 generally giving a smooth type of colony. In this country a large number of 

 Gram-negative cocci have been isolated from the nasopharynx, giving the same 

 sugar reactions, but quite devoid of pigment. Further it has been found that the 



Fig. 109. — Neisseria meimigitidis. Fig. 110. — Neisseria meningitidis. 



Surface colonies on serum agar, 24 Surface colony on serum agar, 7 days, 

 hours, 37^ C. ( X 8). 37° C. ( X 8). 



colonies formed are sometimes smooth and sometimes rough, and that an organism 

 which gives a smooth colony on isolation may subsequently give a rough type 

 of colony. The differentiation of those organisms giving rough colonies from 

 N. pharyngis sicca is in our experience frankly impossible (Wilson, S. P., 1928, 

 Wilson, G. S. and Smith 1928). 



At the moment, therefore, it must be confessed that our ignorance is too 

 great to allow of any satisfactory classification. For provisional purposes the 

 classification on sugar reactions may be used, but this is subject to severe 

 limitations. Briefly, it can be said that N. catarrhalis ferments no sugars, the 

 gonococcus ferments glucose, and the meningococcus glucose and maltose ; the 

 other nasopharyngeal cocci give varied reactions, some being like the menin- 

 gococcus, and others also fermennng sucrose. The Diplococcus crassus can be 

 differentiated by its fermentation of lactose. When first isolated from the body 

 the fermentative reactions of the Gram-negative cocci may be irregular. Nabarro 

 (1917), for example, found that quite a number of meningococci from the cerebro- 

 spinal fluid of children with meningitis failed on first isolation to ferment 



