GIFSQ Tools · Module 4 — Microbiology Methods & Laboratory Operations · Tool 065 of 500
Presence-or-absence workflow. Follow the ISO 6579-1 stages, then enter the samples tested and the number positive to get the detection result for the lot and save it to the on-device log.
Try sample values — fills the form with the worked example below.
Workflow stages
- Pre-enrichment: 25 g sample in buffered peptone water, 37 °C for 18 h.
- Selective enrichment: Rappaport-Vassiliadis broth and Muller-Kauffmann tetrathionate broth.
- Plating: XLD agar and a second selective agar, 37 °C for 24 h.
- Confirmation: biochemical tests and serology on suspect colonies.
Saved results
Saved on this device only — entries stay in this browser and are not sent anywhere.
| Date | Sample | Result |
|---|
–
Positive (%)
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Samples positive
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Result in 25 g
Equation: Prevalence (%) = (samples positive ÷ samples tested) × 100. Result is Detected when at least one sample is positive; Not detected when none is positive. The standard test portion is 25 g.
Method: Salmonella detection, ISO 6579-1. Pre-enrichment in buffered peptone water, selective enrichment in Rappaport-Vassiliadis and Muller-Kauffmann tetrathionate broths, plating on XLD agar, biochemical and serological confirmation.
Assumptions: Each 25 g test portion represents the lot; enrichment recovered any Salmonella present; suspect colonies were confirmed, not just presumed.
Limitations: A negative result means not detected in the portions tested, not proof the whole lot is free of Salmonella; injured cells can be missed without proper resuscitation.
Rounding: Prevalence shown to 1 decimal place; sample counts are whole numbers. Presence-or-absence results are never averaged into a count.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Method: Salmonella detection, ISO 6579-1. Pre-enrichment in buffered peptone water, selective enrichment in Rappaport-Vassiliadis and Muller-Kauffmann tetrathionate broths, plating on XLD agar, biochemical and serological confirmation.
Assumptions: Each 25 g test portion represents the lot; enrichment recovered any Salmonella present; suspect colonies were confirmed, not just presumed.
Limitations: A negative result means not detected in the portions tested, not proof the whole lot is free of Salmonella; injured cells can be missed without proper resuscitation.
Rounding: Prevalence shown to 1 decimal place; sample counts are whole numbers. Presence-or-absence results are never averaged into a count.
This is a calculation aid, not a laboratory report — confirm against your accredited method before citing a value.
Worked example: Five 25 g samples tested, 1 positive. Prevalence = 1 ÷ 5 × 100 = 20.0% — Salmonella detected in the lot, which fails a “not detected in 25 g” criterion.
Enter values above to see results.
Most food criteria for Salmonella are “not detected in 25 g” — a single positive fails the lot. Check the specification for the product. Tool 065 of 500 — GIFSQ
