322 THE CLASSIFICATION OF BACTERIA 



Staphylococcus. — Spherical or ovoid, non-motile, Gram-positive cells, arranged in 

 grape-like clusters on solid media, and in pairs, small groups, or short chains in liquid 

 media. On agar the growth is of a golden, white, or yellow colour. Great variation 

 in biochemical activities, hsemolytic power, and pathogenicity. Actual or potential 

 parasites. 



Type species. Staphylococcus aureus. 



Micrococcus. — Spherical or ovoid cells, non-motile, arranged in pairs, tetrads, or groups, 

 but not in grape-like clusters or chains. Generally Gram-positive. Grow freely on 

 ordinary media. Sometimes produce a yellowish pigment. Gelatin liquefaction is not 

 constant, and is usually slow. Fermentative activities weak. Usually non-pathogenic 

 to man or animals. 



Type species. Microcorrvs Ivlevs. 



Sarcina. — Has same characters as Micrococcus, except that cell division occurs, under 

 favourable conditions, in three planes, so that cubical packets are formed. 

 Type species. Sarcina ventriculi. 



Rhodococcus. — Spherical or ovoid cells occurring in groups or regular packets. Usually 

 Gram-positive, but are easily decolorized. Growth on agar abundant with formation of 

 red pigment. Weak fermentative powers. Gelatin rarely liquefied. Nitrates generally 

 reduced. Saprophytes. 



Type species. Rhodococcus rhodochrous. 



Chroraobacterium. — Small, non-sporing, aerobic rods, usually motile and usually Gram- 

 negative, producing a yellow, red, or violet pigment, which is generally insoluble in water. 

 Saprophytic ; commonly found in water or soil. 



Type species. Chromobacterium violaceum. 



Achroraobacterium. — Motile or non-motile, Gram-negative rods, usually small to 

 medium in size, forming no pigment on agar, and varying in their fermentative abihty. 

 Optimum temperature for growth about 25° C., but often good growth at 37° C. Sapro- 

 phytic ; commonly found in water, soil, and milk. 



Zopfius. — Long rods, occurring in evenly curved chains. Gram-positive. Motile. 

 Spider-web growth on solid media. Facultative anaerobes. Carbohydrates and gelatin 

 not attacked ; hydrogen sulpiride not formed. 



Type species. Zopfius zopfii. 



Proteus. — Highly pleomorphic rods, filaments and curved cells being common in 

 yoimg cultures. Gram-negative. Actively motile. Characteristic spreading growth 

 on moist media. Often Uquefy gelatin, and often produce vigorous decomposition of 

 proteins. Ferment glucose and usually sucrose, but not mannitol or lactose, with pro- 

 duction of acid and gas. 



Type species. Proteus vulgaris. 



Bacterium. — Gram-negative, non-sporing rods : often motile, with peritrichate flagella : 

 some species capsulated. Easily cultivable on ordinary laboratory media. Aerobic and 

 facultatively anaerobic. All species ferment dextrose with the formation of acid, or acid 

 and gas. Many species are active fermenters of a wide range of carbohydrates and allied 

 substrates. Typically intestinal parasites of man and animals, although some species 

 may occur in other parts of the body, on plants, or in the soil. Many species are 

 pathogenic. 



Type species. Bacterium colt. 



Shigella. — Gram-negative, non-motile rods, 2-3 // long by 0-5-0-7 /n broad. Non- 

 capsulated ; non-sporing. Ferment a variable number of carbohydrates with the pro- 

 duction of acid. Lactose is not attacked except by some species, and then not for two 

 days or more. Reduce nitrates to nitrites, form ammonia but not hydrogen sulphide, 



