236 



Microbes and You 



in the statistical table happens to represent you, or someone near 

 and dear to you, the figure has tremendous significance. A single 

 case of disease caused by poor water is one case too many. 



Escherichia coli is a short, gram negative, non spore-forming 

 rod that ferments lactose with both acid and gas production. This 

 is a unique set of reactions reserved for a limited number of organ- 

 isms, and its very uniqueness provides a simple screening technic 

 for determining the presence of sewage. Bacteriological water 

 analysis involves three major steps. 



THE PRESUMPTIVE TEST 

 When tubes of lactose broth are inoculated with water and the 

 tubes are incubated at body temperature, the production of acid 

 and gas through the breakdown of lactose leads the analyst to 



Fig. 38. Presumptive test for the coliform group of organisms in 

 water. The fermentation tubes of lactose broth show gas production in 

 three out of five tubes. The aluminum caps shown here are preferred to 

 cotton plugs by some workers. {From General Bacteriology, D. B. 

 Swingle and W. G. Walter, 2nd ed., Copyright 1947, D. Van Nostrand 

 Company, Inc.) 



