632 



CHROMOBACTERIUM 



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Fig. 129. — Chromobacteri u m prodigiosum. 

 From an agar culture, 24 hours, 37° C. ( X 1000). 

 Left. — Strain showing cocco-bacillary forms. 

 Right. — Same strain from a different culture showing definite rods. 



The colonies on agar are usually homogeneous for the first day or two, and 

 then become differentiated into a convex, pigmented, and 

 relatively opaque centre, and an efiuse, colourless, almost 

 transparent periphery with an irregularly crenated edge. 

 This differentiation results from the secondary outgrowth 

 around the original colony of a film, which may be so thin as 

 to escape observation unless a careful search is made for it. 



In agar stroke cultures there is a raised, confluent, 

 pigmented growth, with a smooth or beaten-copper sur- 

 face, and an undulate or lobate edge. 



In gelatin stab culture there is a moderate, fihform 

 growth extending to the bottom of the tube, usually 

 succeeded by Uquefaction, which may occur rapidly or 

 slowly. In general, the liquid is turbid and granular, and 

 in the upper centimetre or so is pigmented ; below this, 

 out of contact with the air, the growth is colourless. A 

 surface pellicle or ring growth, strongly pigmented, and a 

 slightly pigmented deposit at the bottom of the liquefied 

 gelatin, are not uncommon. 



In broth there is a dense turbidity, generally with a 

 pigmented ring growth or surface pelhcle, and a sUghtly 

 pigmented deposit, which frequently becomes viscous and 

 is difficult to disintegrate on shaking. The broth itself often 

 remains colourless. Multiphcation of the bacilli seems to 

 occur chiefly near the surface ; a membrane forms in con- 

 tact with the air, sinks to the bottom, and is replaced 

 by a fresh membrane. This accounts for the heavy 

 deposit that is generally present after a week. 



Blood serum is frequently liquefied. 

 Resistance. — The organisms of this group are non-sporing, and show no par- 



FiG. 130. — Chromobac- 



teriiim prodigiosum. 



Agar stroke culture, 



24 hours, 37° C. 



