BIOCHEMICAL 753 



of growth with most strains is 25°-46° C, but certain strains, particularly those 

 of the casei type, may grow even at 10° C. Though some of the earlier workers 

 (Rodella 1901) stated that an alkaline was preferable to an acid medium, later 

 workers (Morishita 1929, Weiss and Rettger 1934, Longsworth and Maclnnes 1935) 

 have found that both growth and acid production occur best in the neighbour- 

 hood of pH 6-0, the optimal range being about pH 54-6-8. Pantothenic acid, 

 riboflavin and pyridoxin appear to be important accessory growth factors (Snell, 

 Strong and Peterson 1939). No pigment is produced, but deep colonies in glucose 

 agar often develop a brownish centre, and the agar itself is frequently clouded. 

 Hsemolysin production is variable and has not been studied fully. No toxins 

 are formed. The organisms have very little effect on proteins, and growth on 

 protein media without carbohydrates is very poor. Peterson, Pruess and Fred 

 (1928) have found that they do possess some proteolytic action, as judged by the 

 quantitative estimation of non-protein and amino-acid nitrogen, but according 

 to Kendall and Haner (1924a, 6) this is very slight ; no indole, scatole, or histamine 

 is formed. 



On the other hand they are very active in fermenting carbohydrates. The acid 

 produced from lactose is partly fixed, consisting of laevo- or dextro-rotatory or in- 

 active lactic acid, and partly volatile, consisting of formic, acetic, and butyric acids 

 in the ratio of 6 : 3 : 1 (Curran, Rogers and Whittier 1933). The proportion of 

 volatile to fixed acids varies with different strains from about 4-20 per cent. 

 According to Barker and Haas (1944), however, the intestinal members of the 

 group do not produce lactic acid from lactate, but volatile fatty acids. This type 

 of butyric acid fermentation differs from others in that no appreciable amount of 

 molecular hydrogen and very little CO2 are formed. Malic acid is said to be 

 produced by L. odontolyticus in greater quantity than lactic acid (Mcintosh et al. 

 1924). Gas production is not detectable by the ordinary Durham fermentation 

 tube, except with L. acidophil-aerogenes (Torrey and Rahe 1915), which pro- 

 duces 4-6 volumes of Hg to 1 of COj. Curran, Rogers, and Whittier (1933), 

 however, have shown that most strains produce small quantities of gas from 

 fermentable carbohydrates. The formation of lactic acid from glucose does not 

 require the presence of oxygen or lead to the production of CO 2. Consequently 

 CO 2 is not a major product of fermentation with most strains. An exception to this 

 rule is furnished by L. pentoaceticus, which is able to oxidize lactic to acetic acid 

 (Hunt 1933). In this process one molecule of O2 is used and one molecule of CO 2 

 produced. Hence CO 2 constitutes a more important product of fermentation with 

 this organism than with the other members of the group. The usual products of 

 fermentation, such as alcohol, acetone, acetylmethylcarbinol, and butylene glycol, 

 are not formed (Bertrand and Duchacek 1909). For all practical purposes the 

 organisms may be considered as of the obligatory saccharolytic type. 



Biochemical. — There is considerable variation in the sugars fermented. Glucose 

 and lactose are fermented by practically all strains, maltose and sucrose by a high 

 proportion, mannitol, salicin, and raffinose by a small proportion, while dextrin, 

 inulin, dulcitol, and starch are rarely fermented. Strains of L. bifidus are said, 

 however, to ferment inulin (Weiss and Rettger 1934), and strains isolated from soil 

 and grain are said not to ferment lactose (Hunt and Rettger 1930). Both these 

 statements await confirmation. L. pentoaceticus, the organism described by Fred, 

 Peterson, and Davenport (1919) from silage, sauerkraut, and manure, is peculiar 

 in its ability to ferment xylose. According to Weinstein and Rettger (1932), it is 



