ACIDURIC BACTERIA 421 
ACIDURIC BACTERIA.' 
There is a somewhat poorly defined fijroiip of bacilH, chiefly found 
in the intestinal contents of man and animals,'- many of which possess 
the unusual property of growing in fermentation media of a degree of 
acidity incompatible with the development of all other known bacteria. 
The aciduric bacteria are of two kinds: the true aciduric bacilli, of 
which B. acidophilus is the best known, and facultatively aciduric 
bacteria,^ which are occasionally detected in the intestinal contents 
of man and animals fed for some time upon carbohydrate. The 
facultative organisms rapidly lose their acid to'erance upon cultivation 
in ordinary media, and they are probably to be regarded as examples 
of bacterial adaptation. 
Rahe* distinguishes three types of aciduric bacilli, depending upon 
their action upon carbohydrates. Acid, but no gas is formed, as 
follows : 
Type I. Bacillus bulgaricus (not an intestinal organism) coagulates 
milk, but does not ferment maltose. 
Type II. Coagulates milk and ferments maltose. 
Type III. Does not coagulate milk, but ferments maltose. 
Bacillus Acidophilus.— Bacillus acidophilus, described by IMoro'^ 
and independently by Finkelstein'^ is a somewhat pleomorphic bacillus 
of varying length, which occurs singly or in pairs as a rule. Chain 
formation is not uncommonly observed in cultures on artificial media. 
The organism forms no spores or capsules and 'it is typically Gram- 
positive, although in old cultures a majority of the bacilli are fre- 
quently Gram-negative. 
Isolation and Culture.— The organism may be isolated directly from 
suspected material in 2 per cent glucose broth containing 0.25 per 
cent acetic acid. After two or three days, growth becomes apparent 
and a few loopfuls of the well-shaken culture are transferred to a second 
and then a third tube of the same medium. Usually the third transfer 
contains either a pure culture or it is greatly enriched with the specific 
organism. Pure colonies are obtained by plating upon 2 per cent 
glucose agar unadjusted for reaction, or better, upon glucose agar 
containing 0.2 per cent sodium oleate according to the procedure of 
Salge.^ The addition of proteose peptone to the medium in place of 
ordinary peptone increases the luxuriance of growth materially. 
The colonies are of two types— a round, smooth-edged compact 
colony, and a thin, semi-translucent colony with delicate filamentous 
edges. 
Products of Growth. — B. acidophilus is carbohydrophilic in its activi- 
ties; it does not grow well in media containing proteins and protein 
1 Kendall: Jour. Med. Res., 1910, 22, 153, for resume and literature to 1910. See 
also Rahe: Jour. Infec. Dis., 1914, 15, 141. 
2 Mereshkowsky: Centralbl. f. BakterioL, orig., 1905, 39, 380, 584, 696; 1906, 40, 118. 
3 Kendall: Loc. cit., p. 165. * Loc. cit. 
5 Wien. klin. Wchnschr., 1900, 13, 114. 
'■ Deutsch. med. Wchnschr., 1900, 26, 263. ' Jahrb. f. Kinderh., 1904, 59, 399. 
