56 MEDICAL BACTERIOLOGY 



Morphology. Staphylococci are spherical, unicellular organisms, from 0.5 

 to i .o /x in diameter. The characteristic of their arrangement is irregularity. 

 They occur in masses, some of which resemble bunches of grapes; irregularly 

 arranged groups of three, four and five are numerous; fragmentation of these 

 irregular masses results in accidental arrangement of a few in pairs or short 

 chains as well as singly. 



Motility. In hanging-drop preparations Brownian movement is observed, 

 but not true motility; Staphylococci are non-motile. 



Staining. Staphylococci stain with all the usual anilin dyes and are Gram 

 positive. 



Culture. Staphylococci are aerobic and facultative anaerobic. They grow 

 at any temperature between ioC. and 4bC., most luxuriantly at or near body 

 temperature, 37C. All the ordinary media are suitable for cultivating Staphy- 

 lococci. Media that are slightly alkaline are most favorable, but they grow 

 well if the reaction is neutral or slightly acid. 



Blood Serum.- On coagulated blood serum growth is rapid, at first trans- 

 parent; then, the color becomes rather white, and within 24 to 48 hours chromo- 

 genesis appears. The colonies are round, elevated, smooth-edged and have a 

 moist, glistening appearance. They vary in size, some smaller and a few larger 

 than a pin head, in several days they coalesce and, after a time, slight liquefac- 

 tion of the media is produced by some strains. 



Agar. Growth on agar slants in tubes appears the same as on serum, 

 but liquefaction of agar never occurs. On agar plates colonies appear as al- 

 ready described; they tend to remain discrete; coalescence does not usually 

 occur. 



Gelatin. Surface cultures on plates and slant tubes, incubated at room 

 temperature 2oC. to 25C.) show colonies within 24 to 48 hours. After several 

 days the media adjacent to the colonies liquefies so that each colony is sur- 

 rounded by a basin-like zone of liquid gelatin. As time goes on, liquefaction 

 progresses, zones of liquefaction merge and finally the entire media becomes 

 fluid. 



Gelatin Stab Cultures. First show granular growth along the stab; several 

 days later liquefaction begins. It starts at the surface of the stab; as it pro- 

 gresses it becomes funnel-shaped, the greatest area of liquefaction being at the 

 surface, the track gradually narrowing toward the bottom. A cloudy sediment, 

 white or yellowish, forms in the liquefied gelatin.* 



Bouillon. Becomes cloudy in 12 to 24 hours; then, a white precipitate falls 

 to the bottom, the media continuing cloudy. After several days the sediment 

 becomes yellowish if staphylococcus aureus or citreus is present. 



Milk is acidulated and coagulated. ' 



Potato is the most favorable medium for pigment production. An abundant 



* Different strains of Staphylococci vary in their effect on gelatin nitrates and carbohydrates. 

 Some liquefy gelatin more slowly than others, some do not liquefy it at all. Some act on all the 

 carbohydrates mentioned and others on but one, two or three of them. Some reduce nitrates 

 and others do not. 



