Most Probable Numbers for Evaluation of Coliaerogenes Tests by Fermentation Tube Method

Abstract

In a previous publication (1) a procedure was presented for computation of the most probable number of coli-aerogenes organisms from results of the fermentation tube mnethod of bacteriological analysis of water. Employing this procedure has expedited the computation of most probable numbers corresponding to analytical results possible to be obtained from a wide variety of combinations of portions of sample planted at various dilutions. Such computed values are presented in the accompanying tabulations for the combinations of tubes most likely to be employed in routine water, sewage, and milk analyses. All values are given in organisms per hundred cubic centimeters of sample and are correct to two significant figures. Most probable number (M.P.N.) values in heavy face type are those corresponding to the analytical results in which no skips or apparent inconsistencies occur. Tables 1-A and 1-B comprise values for the results of various combinations of tubes to a total of seven tubes in as many as three dilutions. Table 2 contains the most probable numbers for combinations in which 3, 4, or 5 tubes are planted in each of three dilutions in geometric series, while tables 3-A, 3-B, and 3-C are the most probable number values corresponding to all possible combinations of a total of five tubes when planted in not more than three dilutions in the series 10-1-0.1 cc, 50-10-1 cc, and 100-50-10 cc, respectively.