154 



BACTERIOLOGY FOR NURSES 



STAPHYLOCOCCUS AUREUS 



Morphology and Staining. The organism is a small coccus 

 about 0.8 fi. in diameter, sometimes appearing in pairs or isolated 

 groups of three or four but most commonly in irregular clusters 

 resembling bunches of grapes. It stains with the usual basic 

 anilin dyes. It is Gram positive ; that is, when stained by the 

 method of Gram it retains the gentian violet dye; it does not 

 form spores ; it does not possess flagella and is consequently non- 

 motile, although marked Brownian movement may sometimes be 



noticed in a hanging drop 

 preparation. (Fig. 23.) 



Cultivation. The organisms 

 grow readily on ordinary arti- 

 ficial culture medium made of 

 meat extract. The optimum 

 temperature for growth is 

 about 30 C. although they 

 possess a range from 10 C. to 

 43 C. in which multiplication 

 will occur. In stab cultures in 

 peptone gelatin a line of growth 

 may be observed the day after 

 inoculation, and on the second and third day liquefaction com- 

 mences at the top of the medium. As liquefaction progresses 

 the growth falls to the bottom as a flaky deposit of a golden 

 yellow color, while a yellowish film may remain on the surface. 

 In gelatin plates colonies appear as small yellowish disks around 

 which liquefaction soon commences, giving a cuplike appearance 

 with the small colony mass at the bottom. A stroke culture on 

 agar gives an abundant orange-yellow growth with a smooth 

 shiny surface. Single colonies on agar appear as small disks of 

 the same color. On potato staphylococci grow luxuriantly with 

 an abundant production of pigment ; in broth the growth appears 

 as a turbidity which later settles to the bottom as a sediment. 

 Growth is rapid ; it is estimated that a broth culture may contain 



FIG. 23. Staphylococci. 



