PIGMENT PRODUCTION AND GELATIN LIQUEFACTION 611 



namely a mixture of glucose, salts and fourteen amino-acids, supplemented by 

 the two vitamin constituents just mentioned (Fildes et al. 1936, Knight 1937). 

 According to Kligler, Grossowicz and Bergner (1943), nicotinic acid is the essential 

 factor in the glucose metabolism of Staph, aureus ; thiamin (Bj) acts as a catalyser 

 in the oxidation of pyruvic acid. Riboflavin can apparently be synthesized by 

 the organisms themselves (O'Kane 1941). As with other parasitic bacteria, organic 

 sulphur is necessary for growth ; this is usually obtained in the form of cystine, 

 but methionine and sodium dithiodiacetate can be substituted (Fildes and Richard- 

 son 1937, Gladstone 1937). No growth occurs in the complete absence of COj 

 (Gladstone et al. 1935). (See also Chapter 3). 



Hewitt (1930) has shown that Staph, aureus, when grown in ordinary infusion 

 broth, brings about a rapid fall in electrode potential to between Eh - 0-1 and - 0-2 

 volt. Owing to lack of peroxide formation the potential remains at a low level for 

 a long time, showing no tendency to rise as it does with streptococci. In glucose 

 broth the potential does not fall as low as in ordinary broth. 



Figment Production.^ — ^As already mentioned, the staphylococci are active pig- 

 ment producers. Staphylococcus aureus forms a golden. Staphylococcus citreus 

 a lemon-yellow pigment, while cultures of Staph, albus are of a porcelain-white 

 colour. The development of the pigment and its actual tint depend, however, 

 on several factors. As with many other organisms, the optimum temperature for 

 pigment production does not coincide with the optimum temperature for growth ; 

 more pigment is produced at 22° C. than at 37° C. ; if cultures that have been 

 incubated at 37° C. are subsequently left at room temperature, the colour is seen 

 to deepen. Gelatin and broth are unsuitable. Oxygen is requisite for its develop- 

 ment ; under anaerobic conditions the growth is colourless. Carbon dioxide is 

 said to favour its production, provided oxygen is also present (Lubinski 1894). 

 An agar medium containing 33 per cent, milk is recommended for its study (see 

 Christie and Keogh 1940). 



A very important point to remember is that a given strain of staphylococcus 

 under conditions of artificial cultivation may lose its power of producing pigment. 

 The cause of this loss is unknown. It is most noticeable in the case of Staphylo- 

 coccus aureus, which, when freshly isolated from the animal body, gives a rich 

 golden pigment, but often loses this character on prolonged cultivation. This 

 variation adds greatly to the difficulty of classification, and it must be emphasized 

 that in the study of a particular strain, the property of pigment formation should 

 be noted as soon after isolation as possible (Dudgeon 1908). 



Gelatin Liquefaction. — There is a considerable amount of discrepancy in 

 the reports of various authors as to the power of staphylococci to liquefy gelatin. 

 Of 41 white strains examined by Gordon (1903-4), 24 liquefied gelatin. Kutscher 

 and Konrich (1904) reported upon 57 strains of staphylococci, and found that 

 all liquefied gelatin. Similarly with Klopstock and Bockenheimer (1904) who 

 examined 30 strains, and with Fraenkel and Baumann (1905) who examined 36 

 strains. Dudgeon (1908) found that 44 out of 46 aureus strains and 35 out of 

 56 albus strains liquefied gelatin, while Winslow, Rothberg and Parsons (1920), 

 in examining 180 strains, found that 67 per cent, of the aureus and 47 per cent. 

 of the albus strains liquefied gelatin. 



These discrepancies are to be explained partly by possible difierences in the 

 cocci examined and partly by the length of time during which growth was observed. 



