the maximum dilution of an aqueous suspension of bacteria in which the microorganisms can grow. To determine the bacterial titer, a certain amount of the material being examined, such as soil, water, or food, is placed in a test tube with sterile water and thoroughly mixed. Then 1 milliliter (ml) of the solution in the test tube is diluted tenfold in another test tube. Further dilutions are obtained by repeating the operation many times. By culturing samples of different dilutions in selective or differential diagnostic nutrient media intended for the growth of a given physiological group of bacteria, information may be obtained on the quantity of putrefactive, nitrifying, denitrifying, cellulose, and anaerobic bacteria in the material under study. In the testing of water and food for purposes of hygiene and sanitation, the coli index, or titer of colibacillus (Escherichia coli), is of great importance.
A. A. IMSHENETSKII