BACILLUS LACTIS AEROGENES 



453 



BACILLUS LACTIS AEROGENES 



Bacillus lactis aerogenes is the type of a group which is closely 

 similar to the colon group and often distinguished from it with difficulty. 

 It was first described by Escherich 1 in 1885 who isolated it from the 

 feces of infants. Since then it has been learned that this bacillus is almost 

 constantly present in milk, and, together with one or two other micro- 

 organisms, is the chief cause of the ordinary souring of milk. Apart from 

 its occurrence in milk, moreover, the bacillus is widely distributed in 

 nature, being found in feces, in water, and in sewage. It is distinguish- 

 able from the colon bacillus chiefly by the fact that it is less motile, 

 possesses no flagella, hardly ever forms chains, and, when cultivated upon 

 suitable media, especially milk, it possesses a distinct capsule. It differs 

 from the colon bacillus, furthermore, in that it is capable of fermenting 

 polysaccharids, such as starch, and does not form indol upon pep- 

 ton media. It is distinguishable from the bacillus of Friedlander (B. 

 mucosus capsulatus), according to Wilde, 2 by its more energetic gas 

 formation in dextrose broth, its ability to produce acid on lactose media, 

 and its invariable coagulation of milk. Unlike the colon bacilli, it does 

 not form gas on Dulcit. 3 It differs from the other important non-duleit 

 fermentation, the bacillus acidi lactici, in fermenting saccharose. Ten- 

 tative differentiations of these bacilli may be made as follows: 



It grows upon the simplest media, is a facultative anaerobe, and 

 grows most abundantly at a temperature between 25 and 30 C. 



Upon agar and gelatin it grows with a heavy white growth, the 

 colonies of which have a tendency to confluence and are more mucoid 

 in appearance than are those of Bacillus coli. 



In broth, it causes a general clouding and a pellicle. The cultures 

 have a slightly sour or cheesy odor. 



On potato, the growth is heavy and gas is formed. 



On milk, there is rapid coagulation and acid formation. It is charac- 

 teristic of this bacillus that it is capable of producing a large amount of 

 acid, chiefly lactic, and of being able to withstand these large amounts 

 of acid without being injured by them. 



1 Escherich, Fort. d. Med., 16, 17, 1885. 2 Wilde, Cent, f . Bakt., xx, 1896. 3 Jackswi. 



