88 AIDS TO BACTERIOLOGY 



CHAPTER VII 

 THE COLON-TYPHOID GROUP 



THIS group of bacilli is classed by Loffler as one family, 

 the TypJiaceoB. The characters of individual members 

 are not always clearly defined. As a general rule the 

 organism is short, plump, with rounded ends, often with 

 a tendency to develop long forms. No spores are formed 

 and the organisms are Gram-negative. None liquefies 

 gelatin except B. cloacce and a few coliform organisms 

 described by MacConkey (B. levans, B. oxytocus perniciosus, 

 and his No. 73). On a gelatin plate, they form thin, 

 irregular, notched colonies. All are aerobes and faculta- 

 tive anaerobes, none are chromogenic, and all grow well 

 on ordinary media. 



The Colon Bacillus. 



Bacillus coli (B. coli communis) inhabits the intestinal 

 tracts of man, the lower animals, birds, and, less fre- 

 quently, fish. The dispersion of the dejecta causes this 

 organism to be widely distributed. While a very large 

 proportion of the organisms when isolated are found to 

 conform to the salient characteristics of the recognised 

 type, ' atypical ' organisms are met with which, in one 

 or more respects, differ from the true type. Such are 

 described as ' coliform.' 



Morphology. The colon bacillus is a short rod, 2 JLI to 

 4 ]u long, with rounded ends, but may form much longer 

 rods, or be so short as to be oval in shape. It possesses 

 three or four flagella on an average, and although generally 

 feebly motile, non-motile forms are not uncommon. It 

 forms no spores, and is not stained by Gram's method. 



B. coli is slightly more resistant to heat, to disinfectants 

 and other destructive agents than is B. typhosus. While 

 B. coli does not usually survive an exposure to 60 C. for 

 ten minutes, one variety, B. Griinlhal, produced a toxin 

 that withstood ten minutes at 80 C. According to 

 Ayers and Johnson 54-6 per cent, of cultures survived 

 thirty minutes at 60 C., and 6-9 per cent, survived 

 62-8 C. for thirty minutes. 



