It is expressed as the number of organisms which are most likely to have produced. In the mpn method, a number of tubes showing positive results will estimate the coliform count per 100ml. This number, generated using specific probability form las, is an estimate of the mean density of coliforms in the.
The coliform result for the sample is 26 x 10 = 260 coliforms per 100 ml of sample. After 21 ± 2 hours, tubes are examined for growth and gas production. Gas production in 24 ± 2 hours or less is a positive reaction indicating the presence of fecal coliforms.
The most probable number (mpn) of coliform organisms for the above results is to be obtained using the following mpn index. The results of the confirmed test are as follows: The document shows a table with mpn index and 95% confidence limits for various combinations of positive results from fecal coliform testing methods using multiple tube fermentation. The mpn index from the mpn index table table for 4, 2 and 1 positive tubes is 26.
Because regulations state that coliforms and e. The most probable number (mpn) of coliform or fecal coliform bacteria per unit volume of a sample.