STAPHYLOCOCCUS AUREUS 621 



varying severity in man and animals ; usually it forms a golden-yellow pigment, 

 but alhus variants may be thrown off either in the body or in vitro. It produces 

 toxic filtrates with hsemolytic, leucocytolytic, necrotizing, and lethal properties 

 for the rabbit, and sometimes with irritating properties for the gastro-intestinal 

 tract of man ; it almost always liquefies gelatin, ferments lactose and mannitol, and 

 coagulates plasma ; it contains a specific polysaccharide not possessed by non- 

 pathogenic staphylococci ; its antigenic structure differs from that of the following 

 species. 



Staphylococcus alhus is feebly pathogenic, or non-pathogenic ; it is normally 

 present on the skin, in the hair, and apparently in air, water and dust. It gives 

 porcelain-white or indifferently coloured colonies, but never produces a yellow or 

 golden pigment. It forms no toxin, or does so less frequently than Staph, aureus ; 

 though white variants of Staph, aureus are often highly toxigenic. It frequently 

 liquefies gelatin, but less constantly than Staph, aureus. It often ferments lactose, 

 but not mannitol ; it forms no coagulase ; and it appears to contain, as a rule, 

 a polysaccharide different from that in virulent Staph, aureus strains. 



The third species. Staphylococcus citreus, is a non-pathogenic saprophyte. It 

 produces a distinctive lemon-yellow pigment ; it is doubtful whether it ever forms 

 a toxin ; it liquefies gelatin less frequently and less rapidly than the preceding 

 species. It has little or no fermentative ability ; and it forms no coagulase. 



We append, for purposes of reference, a detailed description of Staph, aureus, 

 together with some of the characters ascribed to those types of staphylococci 

 which have, at various times, received specific names. 



Staphylococcus aureus Rosenbach 



Isolation. — First described fully by Rosenbach (1884). 



Habitat. — Actual or potential parasite found in suppurative lesions of man, in the nose, 

 on the normal skin, and in cow's milk. 



Morphology. — Spherical cells, 0-8-1 -0 /n in diameter ; in cultiu-es on solid media the cocci 

 are arranged in grape-like clusters ; in broth they occur as small groups, pairs, 

 and short chains of not more than fom* members. Stain well with the usual aniline 

 dyes. Non-motile, Gram-positive, non-acid-fast. 



Agar Plate. — 24 hours, 37° C. Circular colonies, 1-2 mm. in diameter, low convex, amor- 

 phous, opaque, and of a golden colour, having a smooth glistening surface and 

 an entire edge ; butyrous in consistency and easily emulsifiable. No differentia- 

 tion visible. 



Agar Stroke. — 24 hours, 37° C. Abundant, confluent, raised, golden-yellow, opaque 

 growth, with a glistening, smooth or slightly contoured surface, and an entire or 

 slightly undulate edge. 



Gelatin Stab. — 5 days, 22° C. Abundant filiform growth reaching to bottom of stab ; 

 siu^ace growth about 5 mm. in diameter ; liquefaction of infundibuliform or saccate 

 type. 



Broth. — 24 hours, 37° C. Moderate uniform turbidity with a moderate, powdery deposit, 

 disintegrating readily on shaking ; slight ring growth at surface. 



Rabbit Blood Agar Plate. — 48 hours, 37° C. Good growth. Blood is partly or completely 

 haemolysed around colonies. 



MacConkey's Agar. — 24 hours, 37° C. Tiny, convex, pinkish colonies about 0-5 mm. 

 in diameter. Later they increase somewhat in size, and take on a deep red 

 colour. 



