364 SOME PROBLEMS IN WATER BACTERIOLOGY 



River. He classified 543 cultures, mostly obtained by isolation on gelatin plates, into 

 17 groups on the basis of their biochemical characteristics. The Illinois River is a 

 rather highly contaminated stream, and the bacterial flora as found by Jordan cannot 

 of course be regarded as the "natural" flora of a surface water, but rather as repre- 

 sentative of conditions existing in a polluted water. As far as the writer is aware, no 

 similar investigation has been made in the past twenty-five years. The attention of 

 water bacteriologists has been focused on a few bacterial groups or species of which the 

 coli-aerogenes group, Clostridium welchii, and the streptococci are the most important. 



COLI-AEROGENES GROUP 



The coli-aerogenes group of bacteria comprises those organisms which are rod 

 shaped, do not form spores, are facultative anaerobes, ferment dextrose and lactose 

 with production of acid and gas, and do not liquefy gelatin. The use of this group of 

 bacteria as an index of sewage contamination of drinking water is too well known to 

 warrant discussion. There are, however, certain differences of opinion in regard to the 

 laboratory procedures employed in sanitary water analysis and the interpretation of 

 the results obtained in the laboratory. If this bacterial group or any particular mem- 

 ber of it is to be used to determine the purity of water supply, there must eventually 

 be unanimity of opinion and practice. The usefulness of standard procedures has al- 

 ready been pointed out. 



The appearance of gas in lactose broth seeded with portions of a water to be tested 

 constitutes the so-called "presumptive" test. It is generally conceded that this test is 

 an inadequate basis on which to judge potable waters. Both anaerobic bacteria and 

 spore-forming aerobes appear in such tests, as well as resistant strains of Bad. coli. 

 Omitting for the moment the questions involving specific members of the coli-aero- 

 genes group, it is obvious that spore-forming bacteria, either aerobic or anaerobic, 

 cannot legitimately be used as indexes of the possible presence of typhoid bacilli on 

 the same basis as other members of the intestinal group of bacteria. Various attempts 

 have been made to inhibit these extraneous bacteria. The most popular method has 

 been by the addition of bile or bile salts to the lactose broth. The early work of Mac- 

 Conkey, of Jordan, Russell, and Zeit,' and of Jackson^ on bile salts was not consistent. 

 Hale and Melia^ advocated the use of lactose bile in the presumptive test and stated 

 that this medium yielded the most satisfactory results. It was for a time adopted as a 

 standard method.^ Jordan,^ however, has shown that bile exerts a marked inhibitive 

 action on Bad. coli. Although some laboratories have continuously employed a bile 

 medium in water analysis, this practice has to a large extent been abandoned. Re- 

 cently, the interest in bile has been revived, particularly in combination with brilliant 

 green. A medium devised by Hale, and containing 5 per cent bile with i : 10,000 bril- 

 liant green, has been used in laboratories for some time. Dunham and Schoenlein* 



' Jordan, E. O., Russell, H. L., and Zeit, F. R.: J. Infect. Dis., 1, 682. 1904. 



' Jackson, D. D.: Biological Studies by the Pupils of William Thompson Sedgwick, p. 292. 1906. 



3 Hale, F. E., and Melia, T. W.: J. Infect. Dis., 7, 567. 1910. 



^ Standard Methods of Water Analysis (2d ed.). 191 2. 



5 Jordan, E. O.: /. Infect. Dis., 12, 326. 1913. 



^Dunham, H. E., and Schoenlein, H. W.: Stain Technol., i, 129. 1926. 



I 



