I. CHARACTERISTICS OF THE COLON GROUP OF BACTERIA* 



The bacteriological analysis of water is an indirect and quantitative 

 one. Specific pathogenic organisms are not sought nor are they likely to 

 be detected even in a dangerous water. It devolves upon the analyst to 

 interpret his findings and particular emphasis is placed on the determination 

 of the presence of the colon group. The investigator and analyst should 

 therefore be thoroughly acquainted with the characteristics, peculiarities, 

 and idiosyncrasies of the organisms in the group, particularly with refer- 

 ence to their distribution, viability, and differential reactions. 



Bacterium coli was first isolated by Emmerich from the feces of a 

 cholera patient in 1884. It was soon recognized as a normal inhabitant 

 of the intestinal tract of man and of other animals. For the past three 

 decades the colon group of bacteria has been extensively studied by bacter- 

 iologists and sanitarians especially those interested in water supply and 

 purification. Probably as much work has been done on this as on any 

 other group of bacteria but there is not as yet an absolute agreement as to 

 the limitations of the group. 



Limitations of the Group. In the 1905 report of the Committee 

 on Standard Methods for Water Analysis of the American Public Health 

 Association a series of tests were described which were supposedly char- 

 acteristic of the colon group. These tests included morphology, motility, 

 fermentation of glucose, coagulation of milk, production of indot, reduction 

 of nitrates, and gelatin liquefaction. Many of these reactions, as gelatin 

 liquefaction, nitrate reduction, and indol formation, require a long incuba- 

 tion period. If the recommendations of the committee were adhered to, 

 it would take at least nine days to justify the inclusion of an organism 

 in the colon group. This was found to be very impractical and the ten- 

 dency has been to simplify the preliminary tests necessary to place an 

 organism in this category. 



The 1917 and the 1920 Standard Methods of Water Analysis define 

 the colon group as follows: "It is recommended that the Bact. coli group 

 be considered as including all non-spore-forming bacilli which ferment 

 lactose with gas formation and grow rerobically on standard solid media." 



This characterization is concurred in by Winslow who defines the 

 colon group as including all aerobic non-spore forming bacilli which produce 

 acid and gas in glucose and lactose media. 



Hauser modifies the definition somewhat by excluding gelatin lique- 

 fiers. 



Other investigators are inclined to extend the colon group to include 

 spore forming organisms which are capable of fermenting lactose with 

 gas production and which grow aerobically on solid media. A few such 

 strains have been recently encountered in the routine examination of water. 

 Perry and Monfort include such spore forming types as members of the 

 colon group. The statement of Lohnis and Smith, who have made studies 



*In conformity with the recommendations of the committee on nomenclature of the 

 Society of American Bacteriologists the colon group is considered in the genus Bacterium. 



