248 Development of a Standardised Agar Medium 



Morphology. (A) Vegetative Cells. (Nutrient agar, Conn, 2 days 

 incubation at 20° C.) The organism consists of short rods, lying singly or 

 in pairs and short chains. Some long rods, up to 10 /a occur. Size of 

 majority 4 x 0-5 /x. The rods are actively motile, and bear 6 to 15 long 

 undulating flagella, which are peritrichous. The organism is gram positive, 

 and takes readily all the usual stains. 



(B) Spore formation. (Nutrient agar, 4 days at 20° C.) Sporangia 

 consist of slightly thickened rods often in chains. Endospores central in 

 position, elhptical, size of majority 1-25 x 0-75)u,. 



Cultural Characters. (A) Agar stroke. (2 days at 30° C.) At first 

 fihform, later (4 days), fiat and spreading. Smooth glistening surface. 

 Growth opaque and whitish. 



(B) Gelatine stab. (2 days at 20° C.) Growth best at surface. Line of 

 puncture filiform. Liquefaction commences in 2 days and becomes napi- 

 form. After 30 days, depth of liquefaction is about 25 mm. 



(C) Potato. (2 days at 30° C.) Abundant, viscid growth of whitish 

 colour. Surface dull and wrinkled. Potato discoloured brown. 



(D) Nutrient Broth. (2 days at 35° C.) Surface pellicle formed. Liquid 

 slightly clouded. No sediment. No odour. 



(E) Agar Colonies. (2 days at 30° C.) Very rapid growth. Colony 

 formation described below. 



(F) Gelatine Colonies. (2 days at 20° C.) Circular with entire edges. 

 Saucer-shaped liquefaction. Rather slow growth. 



Physiology. (A) Fermentation. (Fermentation tubes containing 

 nutrient broth + 1 per cent, of the compound indicated. Incubation 

 4 days at 30° C.) 



Dextrose. Reaction acid (no gas). 



Saccharose. Reaction acid (no gas). 



Lactose. Reaction alkaline (no gas). 



Glycerine. Reaction alkaline (no gas). 



(B) Diastatic Action. (Starch agar plates incubated at 30° C.) Action 

 strong. Breadth of clear zone in 5 days, 5 to 10 mm. 



(C) Litmus Milk. (10 days at 30° C.) No coagulation. No change in 

 reaction or litmus reduction. 



(D) Indol Formation. Negative. 



(E) Nitrate Reduction. (Nutrient broth +0-1 per cent. KNO3 incu- 

 bated at 30° C.) Nitrite present in two days — no gas in 10 days. 



(F) Chromogenesis. Negative. 



(G) The organism is aerobic. Its optimum temperature for growth 

 is about 35° C. 



