Koli-index, coli-titer - quantitative indicators of fecal contamination of water, soil, food products and other objects of the external environment. As an indicator of fecal pollution, a constant inhabitant of the human intestine is used - the E. coli, since it is easily grown under ordinary conditions on simple nutrient media. The number of these bacteria allows us to judge the degree of fecal contamination of the investigated object.
Coli-index - the number of individuals of E. coli, found in 1 liter (for solids in 1 kg) of the object under study; Is determined by counting colonies of Escherichia coli grown on a dense nutrient medium when sowing a certain amount of the test material, followed by recalculation of 1 l (kg). The coli-index is a quantity proportional to the actual content of E. coli in the test substrate.
Coli-titer is the smallest amount of material studied in milliliters (for solids - in grams), in which one E. coli is found. To determine the quantitas, tenfold decreasing volumes of the test material (for example, 100; 10; 1; 0.1; 0.01; 0.001 mL) are separately inoculated into liquid media.
To transfer the colitrum into the coli-index, 1000 should be divided into a number expressing the number; To translate the coli-index into 1000, divide by the number expressing the coli-index.
For technical reasons, the definition of a quantifier is more often practiced.
The determination of colitis (coli-index) is an important criterion in the hygienic assessment of water, food and beverages.