COLON BACILLUS 175 



Cultures. Thrives in all common culture media, especially if 

 sugar is present. It is restrained by excess of acids produced in 

 culture media. On gelatine it grows like the typhoid bacillus 

 (from which it is difficult to differentiate, see page 176) in whitish 

 raised colonies that do not liquefy the media. Sometimes the 

 growth is thin and iridescent, and exhibits bizarre shapes 

 tadpole-like and lobulated. Typhoid colonies show deep furrow- 

 like ridges under the microscope. In the special semi-solid media 

 of Hiss, the typhoid produces uniform cloudiness, with thread- 

 like colonies. The colon does not so quickly cause this cloudi- 

 ness, and forms gas bubbles. On agar plates surface colonies are 

 like typhoid, only they are thicker and moister. If litmus is 

 added to this medium, a red zone forms about the colonies due 

 to the presence of lactic acid. In agar tubes the growth is more 

 luxuriant and resembles typhoid. In litmus bouillon it rapidly 

 reddens the litmus, clouds the medium, and deposits a slimy 

 sediment. In milk it always produces coagulation. On potato 

 it grows more rapidly and luxuriantly than typhoid, at first 

 yellowish-white, which later changes to yellowish-brown. It is 

 slimy. 



Chemical Activities. Produces color on potato only. Sugars 

 are fermented with the production of H, COg and some N. 

 It ferments glucose, lactose, saccharose, maltose, dulcit and 

 some others with the production of gas. Produces lactic, acetic 

 and formic acids, also indol abundantly, and H 2 S. It decomposes 

 urea. 



Habitat. Found always in the intestinal contents of most ani- 

 mals and man. Also in streams and rivers that run through farm 

 lands and by towns. While it is difficult to find typhoid bacilli 

 in contaminated drinking water, the colon bacilli are easily 

 found. If in abundance, it indicates great faecal pollution. In 

 milk it is often found, where it plays an important part in souring. 



Pathogenesis. It is pathogenic to rabbits and guinea pigs, 

 causing peritonitis if injected into the peritoneal cavity. In man 



