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Table 3.
Most probable number (MPN) table (USDA, 2014) for different combinations of positive test tubes for sample volumes of 10 mL, 1 mL, and 0.1 mL, in that order. The MPN index provides a number of bacterial units (cells) per 100 mL. For example, if students confirmed that E. coli was present in 3 tubes containing 10 mL of wastewater, 2 tubes containing 1 mL of wastewater, and 1 tube containing 0.1 mL of wastewater, they would conclude that their sample has an E. coli density of 150 cells per 100 mL.
Combination of PositivesMPN Index per 100 mLCombination of PositivesMPN Index per 100 mL
0-0-0 <3 2-2-0 21 
0-0-1 2-2-1 28 
0-1-0 2-2-2 35 
0-1-1 6.1 2-3-0 29 
0-2-0 6.2 2-3-1 36 
0-3-0 9.4 3-0-0 23 
1-0-0 3.6 3-0-1 38 
1-0-1 7.2 3-0-2 64 
1-0-2 11 3-1-0 43 
1-1-0 7.4 3-1-1 75 
1-1-1 11 3-1-2 120 
1-2-0 11 3-1-3 160 
1-2-1 15 3-2-0 93 
1-3-0 16 3-2-1 150 
2-0-0 9.2 3-2-2 210 
2-0-1 14 3-2-3 290 
2-0-2 3-3-0 240 
2-1-0 15 3-3-1 460 
2-1-1 20 3-3-2 1100 
2-1-2 27 3-3-3 >1100 
Combination of PositivesMPN Index per 100 mLCombination of PositivesMPN Index per 100 mL
0-0-0 <3 2-2-0 21 
0-0-1 2-2-1 28 
0-1-0 2-2-2 35 
0-1-1 6.1 2-3-0 29 
0-2-0 6.2 2-3-1 36 
0-3-0 9.4 3-0-0 23 
1-0-0 3.6 3-0-1 38 
1-0-1 7.2 3-0-2 64 
1-0-2 11 3-1-0 43 
1-1-0 7.4 3-1-1 75 
1-1-1 11 3-1-2 120 
1-2-0 11 3-1-3 160 
1-2-1 15 3-2-0 93 
1-3-0 16 3-2-1 150 
2-0-0 9.2 3-2-2 210 
2-0-1 14 3-2-3 290 
2-0-2 3-3-0 240 
2-1-0 15 3-3-1 460 
2-1-1 20 3-3-2 1100 
2-1-2 27 3-3-3 >1100 
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