STAPHYLOCOCCUS PYOGENES AUREUS 325 



Upon coagulated animal sera, rapid growth takes place and eventually 

 slight liquefaction of the medium is said to occur. 



In nitrate solutions, reduction of the nitrates to nitrites is caused. 



In Dunham's broth, indol is formed. 



In media containing the carbohydrates — dextrose, lactose, or sac- 

 charose — acidification takes place with the formation chiefly of lac- 

 tic, butyric, and formic acids. There is no gas formation, however. 

 In proteid 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.^ 



Pigment Formation. — Differentiation between the various members 

 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. Pro- 

 longed cultivation upon artificial media may lead to a diminution in the 

 depth of color produced.^ It appears only when cultivation is carried 

 oh under freely aerobic conditions, anaerobic cultivation resulting in 

 unpigmented cblonies. The coloring matter is insoluble in water but 

 soluble in alcojhol, chloroform, ether, and benzol.' According to Schnei- 

 der,^ the pigment belongs to the class of " lipochromes '' or fatty pig- 

 ments, and is probably composed of carbon, oxygen, and hydrogen, 

 without nitrogen. Treatment with concentrated sulphuric acid changes 

 it to a green or greenish-blue.^ 



Resistance. — Although not spore formers, staphylococci are more 

 resistant to heat than many other purely vegetative forms. The thermal 

 death point given for Staphylococcus pyogenes aureus by Sternberg" 

 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 re- 

 quired for its destruction. Against low temperatures, staphylococci are 

 extremely resistant, repeated freezing often failing to sterilize cultures. 



^Fr. Mailer, Cent. f. Bakt., xxvi, 1899. 



' Fliigge, "Die Microorg.," etc. 



3 Migula, "System d. Bakt.," Jena, 1897. 



'Schneider, Arb. a. d. bakt. Inst., Karlsruhe, 1, vol. i, 1894. 



» Fischer, " Vorles. tlber die Bakt.," Jena, 1903. 



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



