Meaning and mechanism
Presumptive gas increase prompts follow-up testing, not final coliform detection by itself.
Link confirmed gas, isolated colonies, completed-test lactose gas and morphology within the same tube branch.
Relationships and conditions
Code 1: detected; 0: not detected; −1: pending for missing evidence; −2: test invalid due to control failure.
Do not replace missing values with false; prioritize control failure. The reference does not verify every current official combination.
What to observe in the food simulation
Gas increase alone does not confirm detection. Link follow-up evidence; control failure overrides detection evidence and invalidates the test.
Educational qualitative model food-edu-v1. Coliform results differ from E. coli confirmation and are not converted to CFU or MPN. This does not replace real culture or food safety assessment.
Key relationships and symbols
Δgas = finalGas − initialGas; code ∈ {1, 0, −1, −2}
| Symbol | Meaning | Unit |
|---|---|---|
| Δgas | Gas increase from initial reading | 1 |
| code | Qualitative judgment code | 1 |
| null | Evidence not supplied | 1 |
Worked food-analysis example
Should a missing completed-test result be treated as not detected?
No. Preserve null as not supplied and record pending judgment requiring more evidence. Learning review can still be completed.
Common misconceptions
- Coliform detection is not E. coli confirmation or an assessment of all food hazards.