A CORRELATION STUDY OF THE COLON-AEROGENES 



GROUP OF BACTERIA, WITH SPECIAL REFERENCE 



TO THE ORGANISMS OCCURRING IN THE SOIL 



CHEN CHONG CHEN and LEO F. RETTGER 

 From the Sheffield Laboratory of Bacteriology, Yale University 



Received for publication December 10, 1919 



From the time of the discovery of Bacterium coli and Bacterium 

 aerogenes by Escherich this group of bacteria has been of pro- 

 found interest to bacteriologists and sanitarians. As these organ- 

 isms were first isolated from the human intestine, their presence 

 elsewhere has generally been taken as an index of fecal pollution. 

 They were later found, however, to-be normal inhabitants of the 

 alimentary tract of lower animals covering a wide range of species. 

 The problem became still more complicated when it became 

 known that coli-like organisms are widely distributed in nature, 

 particularly in soil and on plants and cereals. 



For a time it appeared as if the presence of an organism of 

 the B. coli type in water or any other article of human consump- 

 tion was of no sanitary significance. The subject was so confus- 

 ing that one German school of sanitarians entirely discarded the 

 colon test. In spite of this situation, the test for B. coli has 

 been, and is today, strongly advocated and supported by sani- 

 tarians in America, England and France. 



Numerous attempts have been made to devise an acceptable 

 system of classification of the colon-aerogenes group, but with 

 very few exceptions these have failed because they did not rest 

 on a sound basis of natural relationships. In the light of recent 

 researches it becomes quite apparent that difficulties in previous 

 classifications were in large measure due to a lack of delicate and 

 exact methods, neglect in the consideration of normal habitat, 

 and faulty interpretation of results. New methods of study have 

 aroused new interest in this group, however, so that within a 



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