BACILLUS LACTIS AEROGENES 453 



BACILLUS LACTIS A£!R0GENES 



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 bj' Escherich ' 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 non-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,^ by its more energetic 

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

 media, and its invariable coagulation of milk. 



The bacillus is about 0.5 to 1 micron in width and 2 to 4 micra in 

 length. It grows easily upon the simplest media, is a facultative anae- 

 robe, and grows most abundantly at a temperature between 25° and 

 30° C. 



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

 the colonies of which have a tendency to confluence and are distinctly 

 more mucoid in appearance than are those of Bacillus coli. 



In hroth, it causes a general clouding and a pelUcle. 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. 



The pathogenicity of Bacillus lactis aerogenes for man is slight. 

 Its chief claims to importance lie in its milk-coagulating properties 

 and its almost constant presence in the human intestine. In infants, it 

 may give rise to flatulence and it has been occasionally observed as the 



J Escherich, Fort. d. Med., 16, 17, 1885. « Wilde, Cent. f. Bakt., xx, 1896. 



