GIFSQ Tools · Module 3 — Food Microbiology & Enumeration · Tool 046 of 500
Most probable number from a 3-tube test. Enter the positive tubes at each of the three dilutions to read the MPN per gram from the FDA BAM table.
Try sample values — fills the form with the worked example below.
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MPN/g
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95% confidence limit, low
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95% confidence limit, high
Equation: MPN/g is read from the FDA BAM Appendix 2 Table 1 lookup — no arithmetic. The table gives MPN/g and the 95% confidence interval for 3 tubes each at 0.1, 0.01 and 0.001 g inocula.
Method: FDA BAM Appendix 2, Table 1 (3 tubes, 0.1 / 0.01 / 0.001 g). The values are the published table values, to 2 significant figures.
Assumptions: organisms are distributed at random; every tube holding one or more viable organisms shows growth; the three dilutions are consecutive tenfold steps.
Limitations: combinations missing from the table are improbable outcomes — the tool gives no MPN for them and the test should be repeated; MPN is an estimate with a wide confidence interval; 0-0-0 and 3-3-3 are censored (less than 3 / greater than 1100 MPN/g).
Rounding: MPN/g and confidence limits as printed in the table (2 significant figures); no further rounding.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: FDA BAM Appendix 2, Table 1 (3 tubes, 0.1 / 0.01 / 0.001 g). The values are the published table values, to 2 significant figures.
Assumptions: organisms are distributed at random; every tube holding one or more viable organisms shows growth; the three dilutions are consecutive tenfold steps.
Limitations: combinations missing from the table are improbable outcomes — the tool gives no MPN for them and the test should be repeated; MPN is an estimate with a wide confidence interval; 0-0-0 and 3-3-3 are censored (less than 3 / greater than 1100 MPN/g).
Rounding: MPN/g and confidence limits as printed in the table (2 significant figures); no further rounding.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Positive tubes 3, 2 and 1 at 0.1, 0.01 and 0.001 g. The FDA BAM Table 1 entry for 3-2-1 is 150 MPN/g, 95% confidence interval 37 to 420 MPN/g.
Enter values above to see results.
The table covers 3 tubes at 0.1, 0.01 and 0.001 g. For other inocula, multiply the table MPN/g by the factor that makes the inocula match (FDA BAM Appendix 2). MPN is an estimate — always report it with its confidence interval. Tool 046 of 500 — GIFSQ
