46 BACTERIA IN WATER 



BACILLUS COLI COMMUNIS (Escherich) 



Source and habitat An organism of wide distribution, normally present in the 

 excreta of man and animals. Abundant in crude sewage (100,000 per c.c. in 

 London Sewage, Houston). In polluted water, milk, soil, etc. 



Morphology A short rod with round ends; size and shape may vary in same 

 colony; polymorphism, depending upon age of culture, products of culture, com- 

 position of medium, etc., 2 to 3 /z long, 0'5 to 0'6 IM broad ; sometimes oval, hardly 

 longer than broad. Usually single, but occasionally in pairs, bundles, or even 

 chains and threads (Plate 3). 



Staining reaction Ordinary aniline dyes. Decolorised by Gram. (Schmidt 

 states that B. coli from fatty stools of infants holds the Gram.) 



Capsule Present. 



Flagella3 or 4 in number, fragile, short, and not wavy. Sometimes only a 

 terminal one ; sometimes several long ones ; but polar staining and vacuolation 

 frequently present in old cultures, or cultures grown under unfavourable con- 

 ditions. 



Motility Present, especially" in young cultures, but not, as a rule, so active as 

 B. typhosus ; oscillatory rather than progressive. Sometimes apparently absent. 



Spore formation None. 



Biology : cultural characters (including biochemical features} Grows best at 37 C. , 

 but will also grow at room temperature. Gordon showed that many varieties of 

 B. coli exist with many minor modifications (Jour, of Path, and Bact., 1897). 



In gelatine plate cultures the colonies appear generally within 24 hours at 20 C. 

 The deep colonies appear as small white dots, the surface colonies as delicate, 

 slightly granular films of an irregularly circular shape. They are bluish-white by 

 reflected, and amber colour by transmitted light. The diameter of the colony is 

 1 to 2 mm. The colonies are transparent, and sometimes iridescent, especially 

 towards the periphery, but at the centre and over the entire surface in old cultures 

 an opacity due to a greater thickness of the bacterial growth is observed (Plate 4). 



It has been observed that species derived from water grow in transparent 

 colonies, whereas those from the alimentary canal or excreta may show opacity of 

 the colony, which characteristic disappears if the culture be passed through milk. 

 About the second or third day the surface colonies attain a diameter of 5 to 6 mm. , 

 and become marked by concentric, or radiating, or irregular markings. The 

 surrounding gelatine very frequently acquires a dull, cloudy, faded appearance, 

 and the edges of the colony become more crenated and thinner. The whiteness of 

 he colony turns to yellow. There is no liquefaction of the gelatine. 



In gelatine stab-cultures the organism grows rapidly. On the surface, in twenty- 

 four hours, the growth is often 2 to 3 mm. in diameter, and closely resembles a 

 surface colony in a plate culture, though more luxuriant. A thick white growth 

 extends along the whole length of the track of the needle, and not infrequently gas 

 bubbles or fissures appear. The gelatine is not liquefied, even in old cultures. 



In gelatine streak cultures growth is also abundant. In twenty-four hours the 

 elongated milky surface colony may be 5 mm. in diameter. It consists of a delicate 

 faintly-granular film with transparent and irregular margins. Down the centre 

 longitudinally the growth is thicker and therefore more opaque. Irregular thick- 

 enings, foldings, and corrugations may occur in old cultures. Sometimes the film 

 shows iridescence, and the medium, though not liquefied, becomes clouded. The 

 growth, as on the plate cultures, is bluish-white by reflected, and yellowish-amber 

 in colour by transmitted light. 



In 25 per cent, gelatine at 37 C. In 48 hours the melted gelatine remains clear, 

 but a thick pellicle forms on the surface (Klein). 



Gelatine shake cultures become turbid, and within twenty-four hours at 20 C. are 

 riddled with bubbles of gas, which are generally more numerous and larger towards 

 the foot of the tube. They increase in size by the second day, sometimes even 

 forming fissures. The gas is mainly carbonic acid. The presence of a small per 

 cent, of fermentable sugar in the medium increases the gas production (Plate 4.). 

 On potato-gelatine the colonies of B. coli are similar in appearance to those 



