Ames Modified ISO™ Test (MOD-ISO)
A rapid microplate modification of the Ames ISO fluctuation mutagenicity assay — OECD 471 compliant, colorimetric 96-well format, completed in 2–3 days. Detects direct-acting mutagens and pro-mutagens (with S9 activation) using a wide range of Salmonella typhimurium and E. coli tester strains.
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The Ames Modified ISO™ Test (MOD-ISO) is EBPI’s modification of the Ames ISO fluctuation assay, designed to meet OECD 471 Guidelines for the bacterial reverse mutation test. Bacterial tester strains are pre-exposed to differing concentrations of the test compound in suspension for 100 minutes. After exposure, samples are transferred to a 96-well plate with a colorimetric reversion indicator solution, run in triplicate at 5 dilutions, and incubated for 2–3 days.
Mutagenic reversion events cause histidine auxotrophic bacteria to regain the ability to grow, shifting the pH indicator from purple (non-mutagenic / background rate) to yellow (revertant colonies present / mutagenic). The proportion of yellow wells across the concentration gradient is used to calculate mutagenic potency. The test can be run with or without S9 metabolic activation, and includes all controls required for OECD 471 compliance.
- Test organismsSalmonella typhimurium TA98, TA100, TA1535, TA1537, TA1538, TA97a; E. coli WP2 uvrA, WP2 pkm101; YG1024, YG1028
- EndpointHis&sup0; reversion (colorimetric pH indicator): purple = background mutation rate; yellow = revertant colonies (mutagenic)
- Pre-exposure100 minutes in suspension at differing concentrations; triplicate at 5 dilutions
- Format96-well microplate; 48-well evaluation format
- Incubation2–3 days at 37°C
- DetectionColorimetric visual + spectrophotometric; pH indicator colour change purple → yellow
- Metabolic activationCompatible with S9 activation (doubles reagents and plastics included)
- OECD complianceOECD 471 — Bacterial Reverse Mutation Test; all required controls included
📧 Order or Enquire
🍁 Ships from Burlington, Ontario, Canada · International shipping available · S9 versions available on request
MOD-ISO Assay Procedure
The Ames Modified ISO™ Test is completed in 2–3 days. The modification from the traditional Ames plate-incorporation method reduces preparation time while maintaining full OECD 471 compliance.
Pre-Exposure
Bacterial tester strain pre-exposed to test compound at differing concentrations in suspension for 100 minutes at 37°C
Transfer & Plate
Samples transferred and mixed with colorimetric reversion solution; plated onto 96-well plate in triplicate at 5 dilutions
Incubation
Plates incubated 2–3 days at 37°C in sealed Ziploc bags; revertant colonies grow and shift pH indicator colour
Count & Calculate
Count yellow (revertant) vs. purple (non-revertant) wells; calculate mutagenic ratio relative to background and positive controls
Fig. 1 — MOD-ISO 96-Well Plate Result
The photograph below shows a typical Ames MOD-ISO™ result. The assay uses a pH-sensitive colorimetric indicator. Wells containing revertant (mutant) colonies produce acid during bacterial growth, shifting the pH indicator from purple to yellow. The left half of the plate (cols 1–6) shows the background (spontaneous) mutation rate — predominantly purple with occasional yellow wells reflecting normal spontaneous reversion. The right half (cols 7–12) shows the positive mutagenic control — all yellow, indicating complete reversion from full mutagenic activity.
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Reading the Plate Result
Purple — Background / Non-Mutagenic
No reversion occurred at this concentration. The bacterial strain remains auxotrophic (unable to synthesize histidine). Purple wells represent either the background spontaneous mutation rate (in negative control columns) or no mutagenic activity at the tested concentration. A small number of spontaneous purple→yellow transitions is normal and expected.
Yellow — Revertant Colonies / Mutagenic
Reversion has occurred — bacteria have mutated back to histidine prototrophy, grown, and produced acid that shifts the pH indicator to yellow. An increase in yellow wells above background rate indicates mutagenic activity. The positive control (right half) shows complete reversion to yellow across all wells, confirming assay validity.
Three Kit Formats — All Available With or Without Plastics & S9
All three kits use the same MOD-ISO methodology and are available in four configurations each: with or without disposable plastics, and with or without S9 metabolic activation. Contact EBPI to confirm the right combination for your regulatory requirement or budget.
Ames MOD-ISO™ Basic Kit
1 Ames tester strainSingle bacterial strain kit for routine mutagenicity screening. Available with or without plastics, and with or without S9 metabolic activation.
Ordering Options
- 5041-1S — Basic Kit, no plastics, without S9
- 5041-1SP — Basic Kit, with plastics, without S9
- 5041S9-1S — Basic Kit, no plastics, with S9
- 5041S9-1SP — Basic Kit, with plastics, with S9
Reagents Include
- 1 Ames bacterial strain, growth media, and controls
- Reagents for 24 test points (48 with S9)
- Sterile distilled water: 200 mL (basic) / 400 mL (with S9)
Plastics (when ordered with plastics)
- 24 reagent boats — 1 per endpoint (48 with S9)
- 96-well plates, 15 mL tubes, reaction mixture bottle
- Ziploc bags for incubation
Ames MOD-ISO™ Bacterial Strain Kit
2 Ames tester strainsTwo bacterial strain kit for broader mutagenicity profiling. Required for regulatory submissions mandating coverage of both frameshift and base-pair substitution mutations.
Ordering Options
- 5041-2BS-1S — Bacterial Strain Kit, no plastics, without S9
- 5041-2BS-1SP — Bacterial Strain Kit, with plastics, without S9
- 5041S9-2BS-1S — Bacterial Strain Kit, no plastics, with S9
- 5041S9-2BS-1SP — Bacterial Strain Kit, with plastics, with S9
Reagents Include
- 2 Ames bacterial strains, growth media, and controls
- Reagents for 48 test points (96 with S9)
- Sterile distilled water: 400 mL (basic) / 800 mL (with S9)
Plastics (when ordered with plastics)
- 48 reagent boats — 1 per endpoint (96 with S9)
- 96-well plates, 15 mL tubes, reaction mixture bottles
- Ziploc bags for incubation
Ames MOD-ISO™ OECD Kit
5 Ames tester strains · OECD 471Five bacterial strain kit designed to meet OECD Test Guideline 471. S9 metabolic activation is always included. Required for full regulatory submissions.
Ordering Options
- 5041S9-OECD-1S — OECD Kit with S9, no plastics
- 5041S9-OECD-1SP — OECD Kit with S9, with plastics
ⓘ S9 metabolic activation is required for OECD 471 compliance and is included in both OECD kit configurations.
Reagents Include
- 5 Ames bacterial strains, growth media, and controls
- Reagents for 120 test points (5 strains × 24 endpoints each)
- All controls required for OECD 471 compliance
Plastics (when ordered with plastics)
- 120 reagent boats — 1 per endpoint
- 96-well plates, 15 mL tubes, reaction mixture bottles
- Ziploc bags for incubation
Tester Strains — Standard & Specialist
EBPI stocks the standard Ames test strains plus specialist strains for enhanced detection of specific compound classes. Contact EBPI if your required strain is not listed below.
🏢 OECD 471 Compliance — What This Means for Your Submission
The Ames MOD-ISO™ (5041S9-OECD) and Ames 384-ISO™ (6041S9-OECD) are designed to meet OECD Test Guideline 471 for the Bacterial Reverse Mutation Test. This requires: testing with and without metabolic activation (S9), at least 5 concentrations in triplicate, appropriate positive and negative controls, and results expressed as the number of revertant colonies per plate or equivalent. All required controls are included in the OECD kit versions. Contact EBPI to confirm the appropriate kit configuration for your specific regulatory requirement.
⚙️ Metabolic Activation with S9 Fraction — Pro-Mutagen Detection
Many mutagenic compounds require metabolic activation by liver enzymes before they become mutagenically active. The Ames MOD-ISO™ is available in +/− S9 versions that double the reagent and plastic quantities to allow parallel testing with and without S9 activation. The S9 fraction converts pro-mutagens such as benzo[a]pyrene, aflatoxin B1, 2-aminoanthracene, and aromatic amines into their active mutagenic forms, greatly expanding the range of detectable mutagens. S9 Activation Enzymes are available separately (Product No. S9-AMES).
Why Use the Ames MOD-ISO™?
🏢 OECD 471 Compliant
Designed to meet OECD Test Guideline 471 requirements for bacterial reverse mutation testing, supporting regulatory submissions worldwide.
🔬 Microplate Efficiency
96-well colorimetric format processes far more test points per plate than traditional Ames agar plate methods, reducing labour and incubator space.
📉 Objective Colorimetric Readout
Purple/yellow pH indicator provides an objective, unambiguous result that can be read visually or by plate reader — no colony counting required.
⚡ Rapid 2–3 Day Result
Completed in 2–3 days from start to finish — faster than the standard 3-day Ames plate-incorporation protocol in many laboratory workflows.
🧬 Broad Strain Availability
10 standard and specialist tester strains available covering frameshift, base-pair substitution, and specific compound classes. Additional strains available on request.
📋 Ready-to-Use Kits
All reagents, media, controls, and plastics supplied ready-to-use. No preparation of agar, histidine solutions, or top agar required as in traditional Ames methods.
Applications for the Ames MOD-ISO™ Test
Chemicals & Industrial Compounds
Mutagenicity screening of industrial chemicals, process intermediates, solvents, and formulated products for regulatory hazard classification.
Pharmaceuticals & Drug Discovery
ICH S2(R1)-aligned mutagenicity screening during drug development and safety assessment of active pharmaceutical ingredients (APIs) and excipients.
Environmental Samples
Water, wastewater, sediment extract, and air extract mutagenicity — complement with SOS-ChromoTest™ or UMU-ChromoTest™ for a full genotoxicity battery.
Food, Cosmetics & Agrochemicals
Mutagenicity screening of food additives, flavourings, packaging extracts, cosmetic ingredients, and pesticide active substances.
Pro-Mutagen Testing with S9
Detection of compounds requiring metabolic activation — PAHs, aflatoxins, aromatic amines, and other indirect-acting mutagens detected only in the presence of S9 liver fraction.
Research & Education
Used in university and industrial research laboratories across North America. Contact EBPI for educational pricing and protocol adaptations.
Kit Specifications
| Parameter | Detail |
|---|---|
| Product Numbers |
Basic Kit: 5041-1S · 5041-1SP · 5041S9-1S · 5041S9-1SP Bacterial Strain Kit: 5041-2BS-1S · 5041-2BS-1SP · 5041S9-2BS-1S · 5041S9-2BS-1SP OECD Kit (S9 always included): 5041S9-OECD-1S · 5041S9-OECD-1SP (5 strains, 120 test points) |
| Test Method | Modification of Ames ISO fluctuation assay; 96-well microplate colorimetric format; 48-well evaluation |
| Pre-Exposure | 100 minutes in suspension at varying concentrations; triplicate at 5 dilutions |
| Endpoint | His&sup0; → His¹ reversion detected by pH indicator colour change: purple = non-revertant; yellow = revertant (mutagenic) |
| Incubation | 2–3 days at 37°C |
| Test Points | 24 (Basic kit) or 48 (2-strain kit); doubles when S9 activation included |
| Standard Tester Strains | TA98, TA100, TA1535, TA1537, TA1538, TA97a, WP2 uvrA, WP2 pkm101, YG1024, YG1028 |
| Metabolic Activation | +/− S9 available; S9 versions double reagents & plastics for parallel testing |
| Regulatory Compliance | OECD 471 — Bacterial Reverse Mutation Test (OECD kit versions) |
| Detection | Visual colorimetric (purple/yellow) or spectrophotometric plate reader |
| Manufacturer | EBPI — Environmental Bio-Detection Products Inc., Burlington ON, Canada |
Technical Resources
Excel Worksheet
EBPI’s data recording and mutagenic ratio calculation worksheet for the MOD-ISO
⬇️ Download PDFOther Mutagenicity & Genotoxicity Tests
Contact EBPI for pricing, strain selection guidance, OECD version details, or S9 activation options for the Ames MOD-ISO™ Test.