Source: Isolated from dairy products; also from Swiss cheese and buttermilk. Habitat: Dairy products. 3. Propionibacterium rubrum van Niel, 1928. {Bacterium acidi propionici var. rubrum Thoni and Allemann (in part), Cent, f. Bakt., II Abt., 25, 1910, 8; van Niel, The Propionic Acid Bacteria, Haarlem, 1928, 164.) rub 'rum. L. adj. ruber red. Medium sized, stoutish rods to elongated diplococci, 0.8 by 1.2 microns, occurring singly or in pairs, resembling diphtheroids rather than streptococci. Somewhat more slender in media without fermentable car- bohydrate. Aerobic growth occurs as irreg- ular, club-shaped and branched rods. Non- motile. Show metachromatic granules. Gram-positive. Yeast-gelatin-lactate stab: No liquefac- tion. Yeast-agar-lactate stab: Brownish red development in stab, with appreciable dome-shaped surface growth of same color. (Also see Margolena and Hansen, Cent. f. Bakt., II Abt., 99, 1938, 107.) Liquid media: Turbidity in early stages; sediment red and smooth. Litmus milk: Acid coagulation. Indole not produced. Ferments lactic and pyruvic acids, glyc- erol, dihydroxy acetone, glucose, fructose, mannose, galactose, sucrose, maltose, lac- tose, raffinose and mannitol with the pro- duction of chiefly propionic and acetic acids and carbon dioxide. Acid from erythritol, adonitol, arabitol, amygdalin, esculin, salicin, melezitose and trehalose. No acid from d- and 1-arabinose, dextrin, dulcitol, glycogen, inulin, meli- biose, perseitol, rhamnose, sorbitol, starch or xylose. Pantothenic acid and biotin are required for growth; para-aminobenzoic acid is re- quired by some strains and stimulating for others; thiamine, although not required, is stimulating for growth (Delwiche, Jour. Bact., 58, 1949, 396). Nitrites not produced from nitrates. Catalase-positive; very weakly so for aerobically grown cells. Less anaerobic than Propionibacterium freudenreichii and Propionibacterium sher- manii. Distinctive characters: Production of brownish red pigment under anaerobic and aerobic conditions. Fermentation of raffi- nose and mannitol, but not of sorbitol. Source: Isolated from various dairy prod- ucts. Habitat: Dairy products. 4. Propionibacterium thoenii van Niel, 1928. {Bacteritim acidi propionici var. ru- brum Thoni and Allemann (in part), Cent. f. Bakt., II Abt., 25, 1910, 8; van Niel, The Propionic Acid Bacteria, Haarlem, 1928, 164.) thoe'ni.i. M.L. gen. noun thoenii of Thoni; named for J. Thoni, the Swedish bacteriol- ogist who isolated this organism. Description taken from van Niel {loc. cit.) and from Werkman and Brown (Jour. Bact., 26, 1933, 412). Medium sized, stoutish rods to elongated diplococci, 1.0 by 1.5 microns, occurring singly or in pairs, resembling diphtheroids. In media without fermentable carbohy- drate, small, spherical cells occur in short chains. Aerobic growth occurs as irregular, club-shaped and branched rods. Non-motile. Shows metachromatic granules. Gram-posi- tive. Yeast-gelatin-lactate-stab: No liquefac- tion. Yeast-agar-lactate-stab: Brownish red growth throughout stab with appreciable dome-shaped surface growth of same color. Liquid media: Turbidity in early stages; sediment smooth and red. Litmus milk: Mostly acid coagulation. Indole not produced. Ferments lactic and pyruvic acids, glyc- erol, dihydroxy acetone, glucose, fructose, mannose, galactose, sucrose, maltose, lac- tose and sorbitol with the production of propionic and acetic acids and carbon diox- ide. Acid from adonitol, arabitol, erythritol, esculin, salicin and trehalose. No acid from amygdalin, arabinose, dextrin, dulcitol, glycogen, inulin, mannitol, melezitose, meli- biose, perseitol, pectin, raffinose, rhamnose, starch or xylose. Domke (Milchwirtsch. Forsch., 15, 1933,
