388 PATHOGENIC MICROORGANISMS 



In protein media free from sugars, the staphylococcus produces 

 alkali. 



The reducing action of staphylococcus is shown by decolorization 

 in cultures of litmus, methylene-blue, and rosanilin. 4 



Pigment Formation. Differentiation between the various mem- 

 bers of the staphylococcus group is based largely upon the formation 

 of pigments. These pigments, so far as we know, seem to be species 

 characteristics. Thus, Staphylococcus pyogenes aureus is recognized 

 primarily by its production of a yellowish-brown pigment, varying 

 in different strains from a pale brown hue to a deep golden yellow. 

 Prolonged cultivation upon artificial media may lead to a diminution 

 in the depth of color produced. 5 It appears only when cultivation is 

 carried on under freely aerobic conditions, anaerobic cultivation 

 resulting in unpigmented colonies. The coloring matter is insoluble 

 in water but soluble in alcohol, chloroform, ether, and benzol. 6 

 According to Sch'neider, 7 the pigment belongs to the class of "lipo- 

 chromes" of fatty pigments, and is probably composed of carbon, 

 oxygen, and hydrogen, without nitrogen. Treatment with concen- 

 trated sulphuric acid changes it to a green or greenish-blue. 8 

 Neisser 9 states that the pigment of staphylococci is excreted into the 

 media by the organisms but does not diffuse because it is not soluble 

 in water. Differences in pigment have been the basis of differentia- 

 tions within the micrococcus group as we shall see below. 



Resistance. Although not spore formers, staphylococci are more 

 resistant to heat than many other purely vegetative forms. The 

 thermal death point given for Staphylococcus pyo genes aureus by 

 Sternberg 10 lies between 56 and 58 C., the time of exposure being 

 ten minutes. The same author states that, when in a completely 

 dried state, the coccus is still more resistant, a temperature of from 

 90 to 100 C. being required for its destruction. Against low tem- 

 peratures, staphylococci are extremely resistant, repeated freezing 

 often failing to sterilize cultures. 



Desiccation is usually well borne, staphylococci remaining alive 



4 Fr. Muller, Cent. f. Bakt., xxvi, 1899. 



5 Fliigge, ' ' Die Microorg., ' ' etc. 



*Migula, tl System d. Bakt.," Jena, 1897. 



7 Sclmeider, Arb. a. d. bakt. Inst,, Karlsruhe, 1, vol. i, 1894. 



s Fischer, "Vorles. iiber die Bakt,," Jena, 190,,. 



9 Neisser, Kolle and Wassermann, 2nd Ed. vol. 4, p. 369. 



10 Sternberg, "Textbook," etc., N. Y., 1901, p. 375. 



