CHAPTER XVII. 

 THE COLI CLOACA PROTEUS GROUP. 



BACILLUS COLL 



Historical. Bacillus coli was isolated in pure culture from the 

 feces of infants, and its important cultural characters determined by 

 Escherich in 1886. 1 It is very probable, as Escherich suggested, 2 

 that Emmerich's B. neapolitanus, Brieger's "propionic acid bacillus," 

 and Frankel's bacilli 3 are identical with the colon bacillus. 



Morphology. Bacillus coli is a rod-shaped organism which varies 

 in shape from oval organisms resembling cocci to bacilli of moderate 

 length. The organism varies in size from 0.5 to 0.8 micron in dia- 

 meter and from 1 to 3 microns in length. The bacilli occur singly and 

 in pairs; in older cultures short chains and elongated organisms are 

 frequently observed. The ends are distinctly rounded. Motility is 

 variable; many strains are non-motile except during the earlier hours 

 of growth. Young cultures on gelatin are said to exhibit motility 

 when older growths even in the same medium are motionless except 

 for Brownian movement. Very commonly only a very few organisms 

 in a microscopic field exhibit motion, the remainder being without 

 movement. Four to eight peritrichic flagella are commonly attached 

 to each bacillus; less frequently as many as twelve may be demon- 

 strated. The flagella are somewhat shorter than those of the typhoid 

 bacillus and they are more difficult to stain. Bacillus coli forms no 

 spores nor capsules. It stains readily with the ordinary anilin dyes, 

 ard it is uniformly Gram-negative. 



Isolation and Culture. The colon bacillus grows readily on the ordi- 

 nary media; the superficial colonies on agar plates are clear and color- 

 less and attain a diameter of from 2 to 5 mm. after eighteen hours' 

 incubation at 37 C. If the surface of the medium is moist the edges 

 of the colonies are somewhat irregular in outline; on dry surfaces the 

 colonies are round and slightly convex in section. Viewed by trans- 



1 Die Darmbakterien des Sauglings, Stuttgart, 1886, 63. 



2 Loc. cit., 73, 74. 



3 Deutsch. med. Wchnschr., 1885, Nos. 34 and 35. 

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