METABOLISM AND BIOCHEMICAL CHARACTERS 633 



ticular resistance to heat or disinfectants. They appear to be. killed by a temper- 

 ature of 55° C. in 1 hour. 



Metabolism and Biochemical Characters. — All the members are markedly 

 aerobic, growing best in the presence of an ample supply of oxygen. Growth under 

 anaerobic conditions is poor, and is not accompanied by pigment formation. 



Proteins are broken down readily as a rule ; gelatin, casein, and often blood 

 serum are digested. Carbohydrates are attacked freely by some, sparingly by 

 others, generally with the production of acid only. 



Growth can be obtained on synthetic media devoid of protein. The optimum 

 temperature of growth is between 25° and 37° C, but some strains will grow as low 

 as 0° C. 



All form catalase and reduce methylene blue. Indole is rarely produced ; the 

 M.R. and V.P. reactions are generally negative. Nitrates are often reduced to 

 nitrites ; and ammonia is generally formed from peptone. Formation of HjS is 

 slight or absent. 



Pigment is produced only in the presence of oxygen, and at a suitable tem- 

 perature. The optimum temperature for pigment formation does not necessarily 

 correspond with that for growth. Thus many organisms grow best at 30-37° C, 

 but form little or no pigment, whereas at a lower temperature growth is poorer, 

 but pigment formation is abundant. Pigment is developed best on the surface 

 of solid media ; in broth and in the depths of stab cultures there is little or 

 none formed. Potato is a medium that may be specially recommended for the 

 study of pigment production. As a rule pigment is formed most abundantly on 

 primary isolation ; after subculture in the laboratory for some time, the power 

 to form it may diminish seriously, or be altogether lost. Not all bacilli in a given 

 culture produce the same amount of pigment ; some colonies are deeply coloured, 

 others are faintly or partly coloured, while still others are completely colourless. 



Sullivan (1905-6) states that the formation of pigment is dependent on the 

 reaction of the medium, the temperature, the free access of oxygen, and the presence 

 of certain salts. In synthetic media, asparagin, succinic, lactic and citric acids, 

 when combined with an ammonium base, allow of growth and pigment formation. 

 Mahc, tartaric, and oxaHc acids, combined with ammonia, allow of growth but 

 not of pigment production. Acetic, uric, and formic acids, combined with ammonia, 

 are unfavourable for both growth and pigment production. (This refers to solutions 

 of 0-4 per cent, or under.) The salts favouring the production of pigment serve 

 either to provide nutrient material, or to fix the acid produced, or to afford material 

 for essential syntheses. 



Pathogenicity. — -The organisms of this group are essentially saprophytic. A 

 few doubtful cases of suppuration in man have been described (see Schiitz and Laun 

 1933), but generally speaking these organisms do not give rise to natural disease in 

 man or in animals. On experimental inoculation into laboratory animals they prove 

 harmless except in very large doses. 



Variation. — It is convenient to mention here that the characters of a single 

 strain are Uable to considerable variation. Its cultural appearances are by no 

 means uniform ; colonies may vary in their size, shape, opacity, surface, and 

 consistency. 



In their abihty to produce pigment there is likewise great variation. From 

 7 different strains of Chr. prodigiosum and Chr. kielense, Eisenberg (1914) isolated 



