624 MICROCOCCUS, SARCINA, RHODOCOCCUS AND LEVCONOSTOO 



carbohydrates. Grows between 6° C. and 36° C. ; optimum temperature 22° C. Is 

 distinguished by the fact that it forms a yellow pigment only when it is exposed to light 

 — sunlight or diffused daylight ; when kept in the dark the growth is colourless. 



(5) Micrococcus coronatus Fliigge. — Described by Fliigge (1896). A coccus 1 /n in 

 diameter, occurring in groups or short chains, Gram-positive. On gelatin plates in two 

 days it forms whitish points ; around these there appears a fresh growth, which later 

 becomes separated from the colony by a clear ring of liquefaction. The central part 

 assumes a dark brown, the peripheral a yeUowish-brown colour. It is the halo around 

 the colony which gives the organism its name. Found in air. 



(6) Micrococcus caseolyticus Evans (1916). This organism is similar in many respects 

 to M. coronatus. It occurs in large clumps, is generally Gram-positive, and is found in 

 milk, milk products, and in the udder of the cow. It produces a luxuriant white growth 

 on agar slants. It liquefies gelatin, and reduces nitrates. It produces an acid curd in 

 mUk and peptonizes it rapidly. It generally utilizes ammonium salts as the sole source 

 of nitrogen, and usually produces acid in glucose and lactose. 



(7) Micrococcus radiatus Fliigge. — De- 

 scribed by Fliigge (1896). Small coccus, less 

 ,• than 1 /t in diameter, occurring in small 



groups, or sometimes short chains. On 

 * gelatin plates the colonies after 2 days are 



about 1 mm. in diameter, whitish in colour, 

 ^» .. * with a shghtly irregular edge. During the 



"^ next two days outgrowths occur radiating 

 ,, i, ■ > from the centre in an orderly manner, so 



^ " that the colony assumes an appearance not 



*■ *" - ^ unlike that of a starfish ; meanwhile lique- 



#• faction sets in, and the centre sinks gently 



„ into the medium. The ends of the out- 



'^ growths are joined together by a ring of 



growth, from which after another two days 

 *• ^ ^^^ fresh radiations may arise, and from these 



yet a third set. When fully grown, the 



Fig. l28.~Micrococcustetragenus ^^j ^^^ ^ diameter of 1-0-1 -5 cm. In a 



1 rem an agar culture, 24 hours, 37 C. . .*' , , , • i , , 



(X 1000). gelatm stab, the colomes down the stab 



send out horizontal shoots, giving the growth 

 a feathery appearance ; on the surface there is a slow liquefaction of infundibuUform 

 type. 



(8) Micrococcus urese Cohn (1875) is a spherical organism, occurring singly, in pairs, 

 or in short chains. Diameter 0-8-1 -0 fj,. Gram-positive, though often weakly so. On 

 agar it forms whitish, low convex, opaque colonies. Gelatin is not liquefied as a rule. 

 Nitrates not reduced. Can utilize urea and ammonium salts as sole source of nitrogen. 

 Found in stale urine. 



(9) Micrococcus freudenreichii is closely related to M. urece. It is a facultative parasite. 

 Cells occur singly or in clumps. Generally Gram-positive. Liquefies gelatin, but does 

 not reduce nitrates. Does not usually produce sufficient acid to curdle milk. Can utilize 

 ammonium salts, but not urea, as the sole source of nitrogen. Is one of the commonest 

 non-pigment-producing micrococci in milk and dairy utensils. 



(10) Micrococcus tetragenus Gaffky. — First described by Gaffky in 1883. It was 

 isolated by Koch from lung cavities in patients vnth pulmonary tuberculosis. Gram- 

 positive, spherical organism, dividing in two planes at right angles to each other, so that 

 tetrad forms are produced. In the human and animal body a capsule is formed. Grows 

 freely on ordinary media. Optimum temperature for growth is 37° C. The growth on 

 agar is of a glutinous consistency, often adherent to the medium, and difficult to emulsify. 



