634 CHROMOBACTERIUM 



no fewer than 22 variants, differing in colour from dark red to red, orange-red, 

 pink, pale-pink, pinkish-white, and colourless ; most of these remained stable on 

 subculture. From Clir. violaceum 5 variants were obtained. Eisenberg found 

 that variants appeared most readily in ageing cultures, and more rapidly in fluid 

 than in solid media. 



Group Producing a Violet Pigment. — Chr. violaceum, the chief member of the 

 group, is a common inhabitant of water. The violet pigment is soluble in alcohol, 

 but insoluble in water, chloroform, or benzol. For its formation in synthetic 

 media both magnesium sulphate and a phosphate are required. On subculture 

 the organism frequently loses its pigment-forming power. We append a detailed 

 description of this organism, together with brief accounts of some of the other 

 violet-pigment-producing members. 



Chromobacterium violaceum 



Synonym. — B. violaceus. 



Isolation. — Described by Bergonzoni in 1881 (see Text). 



Habitat. — Water. 



Morphology. — Rods ; 1-5-3-0 /i X 0-6 // ; axis straight, sides parallel, ends rounded ; 

 arranged singly. Motile by peritrichate flagella. Non-sporing ; non-capsulated. 

 Gram-negative, non-acid-fast. May show bipolar staining. 



Agar Plate. — 2 days at 37° C. Round colonies, |-1 mm. in diameter, low convex, violet 



coloured, translucent, with a smooth glistening 

 surface and an entire edge ; butyrous consistency 

 and easily emulsifiable ; structure appears floccu- 

 lar. After 5 days colonies are larger, 1-2 mm. in 

 diameter, have a finely lobate edge, and are 

 differentiated into a dark convex centre, and a 

 paler, flattened, radiate periphery. 

 Agar Slope. — 2 days, 25° C. Moderate growth, raised, 

 violet, opaque, with glistening, smooth or beaten- 

 copper surface and an undulate edge. Medium 

 unchanged. 



Gelatin Stab. — 5 days, 20° C. Moderate, filiform growth 

 Fig. 131. — Chromobacterium . ■> ^, t ^ -u -i^ t ^i, i^ 



violaceum *° bottom of stab ; violet surface growth ; slow 



„ , , ,„ infundibuliform or saccate liquefaction ; liquefied 



Surface colony on agar, 48 . . , , • i ^ 



hours, 22° C. ( X 8). portion is granular and \nolet. 



Broth. — 2 days, 25° C. Abundant growth, with dense 

 colourless turbidity ; a violet ring growth, and a moderate viscous deposit 

 disintegrating on shaking. Mawkish odour. 



Blood Serum. — 9 days, 25° C. Moderate, confluent growth, colourless, with an uneven 

 surface. Digestion is very slow, or may be absent. 



Potato.— Q days at 25° C. Abundant, raised, confluent, creamy growth of violet colour, 

 with smooth or contoured gUstening surface. 



Resistance. — Killed by 55° C. in 1 hour. 



Metabolism. — Aerobic ; shght colourless growth anaerobically. Opt. temp. 25° C. Pig- 

 ment formation best at 25-30° C. Pigment : soluble in alcohol, insoluble in 

 chloroform or water. 



Nutritional. — Grows well on ordinary media. In synthetic media, pigment is formed 

 only in the presence of MgS04 and a phosphate. 



Biochemical. — Sometimes acid in glucose and maltose. Indole— or shght-]-. 

 M.R. — . V.P. — . Nitrate reduction -[-. NH34-. Catalase-f. M.B. reduc- 

 tion +. HjS shght +. L.M. 6 days 25° C. alkaUne, violet ring growth; later 

 may be coagulated, and slowly peptonized. 



