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Maximum Recovery Diluent (MRD, Tryptone Salt Broth) AS-1411 | Ausamics
$77.00 AUD
Maximum Recovery Diluent (MRD)
ISO 6887 Isotonic Diluent for Food, Dairy & Environmental Microbiology | Tryptone Salt Broth | Cat. No. AS-1411
Cat. No. AS-1411 pH 7.0 ± 0.2 9.5 g/L Tryptone 1 g/L | NaCl 8.5 g/L ✓ ISO 6887-1 to -5 ✓ Merck 0120635 Equivalent ✓ Oxoid CM0989 Equivalent 🇦🇺 Made in Melbourne ⚡ Same-Week Dispatch
Cat. No.
AS-1411
pH (25°C)
7.0 ± 0.2
Dissolution
9.5 g/L
NaCl
8.5 g/L (isotonic)
Sterilisation
121°C / 15 min
📄 Full DocumentationCOA, TDS & SDS every batch
🇦🇺 Australian StockNo import delays
⚡ Same-Week DispatchMelbourne warehouse
🔬 Technical SupportDirect from our team
Overview — What Is MRD and Why Does It Matter?
Maximum Recovery Diluent (AS-1411) is the standard isotonic diluent specified in ISO 6887-1 to 5 for the preparation of test suspensions and decimal dilution series in food, dairy, water, and environmental microbiology. It is also widely known as Tryptone Salt Broth or Universal Diluent.
Its formulation — Tryptone (1 g/L) combined with physiological saline (NaCl 8.5 g/L) — is carefully calibrated to do two things simultaneously: protect microorganisms from the physical stresses of dilution, and not promote significant cell multiplication during the 1–2 hours typically required to prepare and plate samples. Both properties are equally important for accurate viable count results.
Why "Maximum Recovery" — The Science
The problem with simple diluents: Pure water, distilled water, or even physiological saline (0.9% NaCl alone) causes osmotic and hypotonic stress in microorganisms during dilution — particularly sublethally injured cells that have already been damaged by heat treatment, chilling, freezing, desiccation, preservatives, or sanitiser exposure. These stressed cells may lyse or lose viability in an inadequate diluent, leading to an undercount of the true viable population.
How MRD solves this: The low concentration of Tryptone (1 g/L) provides a minimal protective peptide and amino acid environment that stabilises the bacterial cell membrane and reduces osmotic shock. The 8.5 g/L NaCl maintains isotonic conditions closely matching bacterial cytoplasmic osmolarity (~290 mOsm/kg). Together, these components preserve stressed organisms through the dilution process — maximising the recovery of the true viable count on the subsequent plating step.
Why not a richer medium? Higher nutrient concentrations (as in Buffered Peptone Water or TSB) would allow cells to begin multiplying during sample preparation, inflating the viable count. At 1 g/L Tryptone, MRD maintains cells without permitting significant division within the 1–2 hour working window.
How MRD solves this: The low concentration of Tryptone (1 g/L) provides a minimal protective peptide and amino acid environment that stabilises the bacterial cell membrane and reduces osmotic shock. The 8.5 g/L NaCl maintains isotonic conditions closely matching bacterial cytoplasmic osmolarity (~290 mOsm/kg). Together, these components preserve stressed organisms through the dilution process — maximising the recovery of the true viable count on the subsequent plating step.
Why not a richer medium? Higher nutrient concentrations (as in Buffered Peptone Water or TSB) would allow cells to begin multiplying during sample preparation, inflating the viable count. At 1 g/L Tryptone, MRD maintains cells without permitting significant division within the 1–2 hour working window.
Applications
🍕
Food Microbiology
ISO 6887 serial dilutions for food TVC and pathogen testing
🥛
Dairy Testing
Milk, cheese, yoghurt, dairy product dilution
🌿
Environmental
Swab, surface, soil, and water sample dilution
💧
Water Microbiology
Sample homogenate preparation for water testing
💊
Pharmaceutical QC
Non-sterile product dilution for USP/EP microbial limit testing
🏭
Industrial QC
Processing environment surface sampling and viable counts
MRD vs Other Common Diluents
✓ MRD (AS-1411) — This Product
Tryptone 1g/L + NaCl 8.5g/L. ISO 6887 standard. Best for stressed/injured organisms. 1–2h working window. Preferred for food and dairy.
Buffered Peptone Water (AS-1139)
Peptone 10g/L + buffers. ISO 6579 (Salmonella). Pre-enrichment only — too nutritious as a diluent (promotes growth).
Peptone Water (0.1%)
Peptone 1g/L only, no salt. Less osmotic protection than MRD. Older method; ISO 6887 now prefers MRD.
Physiological Saline (0.9% NaCl)
NaCl 9g/L, no peptone. No membrane protection. Acceptable for robust organisms but not recommended for injured cells.
Ringer's Solution (1/4 strength)
Multi-salt isotonic solution. Some standards reference this but ISO 6887 specifies MRD as the primary diluent.
ISO 6887 Application Scope
ISO 6887-1:2017 — General rules for preparation of test samples, initial suspension and decimal dilutions
ISO 6887-2:2017 — Meat and meat products
ISO 6887-3:2017 — Fish and fishery products
ISO 6887-4:2017 — Dairy products and dairy processing environment
ISO 6887-5:2020 — Surface samples obtained by contact plates and swabs
MRD (Tryptone 1 g/L + NaCl 8.5 g/L, pH 7.0) is the specified primary diluent across all five parts.
ISO 6887-2:2017 — Meat and meat products
ISO 6887-3:2017 — Fish and fishery products
ISO 6887-4:2017 — Dairy products and dairy processing environment
ISO 6887-5:2020 — Surface samples obtained by contact plates and swabs
MRD (Tryptone 1 g/L + NaCl 8.5 g/L, pH 7.0) is the specified primary diluent across all five parts.
FAQs
❓ Why does MRD protect stressed microorganisms better than saline alone?
Saline (0.9% NaCl) provides osmotic balance but no membrane stabilisation. Sublethally injured bacteria — damaged by heat, cold, desiccation, sanitisers, or preservatives — have compromised membranes that are vulnerable to the dilution process itself. The 1 g/L Tryptone in MRD provides short peptides and amino acids that stabilise and partially repair these damaged membranes, maintaining cell integrity through the dilution and holding period before plating. This is why MRD recovers more viable cells than saline alone from processed or stressed food samples.
❓ How long can I hold diluted samples in MRD before plating?
ISO 6887-1 recommends that the time between preparation of the first dilution and inoculation of the agar plates should not exceed 45 minutes at room temperature (20–25°C). Some validated methods allow up to 1–2 hours. At 1 g/L Tryptone, cell multiplication is negligible within this window — but viable counts will drift if samples are held too long, particularly for rapidly growing organisms. For stressed organisms, plate as quickly as possible after preparation to maximise recovery.
❓ Can I use MRD instead of Buffered Peptone Water for Salmonella pre-enrichment?
No — these are different purposes. MRD is a diluent, not an enrichment medium. Buffered Peptone Water (BPW, ISO 6579) contains 10 g/L peptone and pH buffers designed to allow Salmonella to recover and multiply during a pre-enrichment step. Using MRD (1 g/L peptone) for Salmonella pre-enrichment would be inadequate and non-compliant with ISO 6579. Use BPW (AS-1139) for Salmonella pre-enrichment and MRD for decimal dilutions before plate counting.
❓ Why is NaCl 8.5 g/L rather than 9 g/L (physiological saline)?
8.5 g/L NaCl (~145 mM) is the ISO 6887 specification and represents the osmolarity at which the combined Tryptone + NaCl solution is isotonic for the broadest range of food-associated microorganisms. Standard physiological saline (0.9% = 9 g/L) is formulated for mammalian cell applications and is slightly higher than optimal for many bacterial species. The 8.5 g/L NaCl in MRD is consistent across Merck/Millipore 0120635, Oxoid CM0989, BD Difco 218971, and all ISO-reference commercial preparations.
❓ Is AS-1411 equivalent to Merck 0120635 and Oxoid CM0989?
Yes — AS-1411 follows the same ISO 6887 specification: Tryptone (Pancreatic Digest of Casein) 1.0 g/L, Sodium Chloride 8.5 g/L, pH 7.0 ± 0.2, dissolution 9.5 g/L, autoclave 121°C / 15 min. Full COA supplied with every batch for side-by-side verification.
Cross-Reference / Equivalents
| Manufacturer | Product Name | Cat. No. |
|---|---|---|
| Merck / Millipore | Maximum Recovery Diluent | 0120635 |
| Thermo Scientific / Oxoid | Maximum Recovery Diluent | CM0989 |
| BD Difco | Maximum Recovery Diluent | 218971 |
| HiMedia | Maximum Recovery Diluent | M1030 |
| Scharlau Microbiology | Maximum Recovery Diluent | 02-510 |
Related Products
Product Specifications
| Product Name | Maximum Recovery Diluent (MRD) |
| Catalogue Number | AS-1411 |
| Synonyms | Tryptone Salt Broth; Universal Diluent; Peptone Salt Solution; Tryptone Sodium Chloride Solution; ISO Diluent |
| Regulatory Standard | ISO 6887-1:2017 to ISO 6887-5:2020 — specified primary diluent |
| Commercial Equivalents | Merck/Millipore 0120635 | Oxoid CM0989 | BD Difco 218971 | HiMedia M1030 | Scharlau 02-510 |
| Medium Type | Isotonic protective diluent (liquid, no agar) |
| Dissolution | 9.5 g/L in distilled or deionised water |
| Final pH at 25°C | 7.0 ± 0.2 |
| Sterilisation | Autoclave 121°C for 15 minutes |
| Appearance (powder) | Cream to light beige, free-flowing homogeneous powder |
| Appearance (prepared solution) | Clear, colourless to very pale straw; no precipitate |
| Storage (powder) | Below 30°C, dry, tightly sealed, away from light |
| Storage (prepared solution) | 2–8°C; use within 2 weeks of preparation |
| HS Tariff Code | 3821.00.00 |
Formula — Per Litre (ISO 6887 Reference)
| Ingredient | g / L | Function |
|---|---|---|
| Tryptone (Pancreatic Digest of Casein) | 1.0 | Minimal protective peptides and amino acids — stabilises stressed cell membranes without promoting significant multiplication within the 1–2h working window |
| Sodium Chloride (NaCl) | 8.5 | Maintains isotonic conditions (~145 mM) — prevents osmotic shock during dilution of food and environmental samples |
| Total | 9.5 g/L | pH 7.0 ± 0.2 at 25°C — Autoclave 121°C / 15 min — Clear colourless solution |
ⓘ The simplicity of this formula is deliberate. Two components, precisely balanced — enough to protect, not enough to enrich. Any modification (increasing peptone, adding phosphate buffer) changes the fundamental protective-to-non-proliferative balance that defines MRD. Use AS-1411 as specified for ISO 6887 compliant methods.
Preparation Protocol
1
Suspend 9.5 g of dehydrated MRD (AS-1411) in 1 litre of purified or distilled water.
2
Mix thoroughly until completely dissolved. Gentle heating may be used if necessary — the powder dissolves readily at room temperature.
3
Dispense into tubes, bottles, or flasks at the required volumes (typically 9 mL per tube for 1:10 dilutions, or 90 mL per bottle for 1:10 initial homogenisation).
4
Sterilise by autoclaving at 121°C for 15 minutes. Allow to cool before use.
5
Check for clarity after autoclaving — prepared MRD should be clear and colourless. Discard if turbid or precipitate is visible.
⚠️ Holding time: Per ISO 6887-1, plate within 45 minutes of preparing the first dilution at 20–25°C. Prolonged holding allows viable counts to change, particularly for rapidly growing organisms or very contaminated samples.
ISO 6887 Serial Dilution Protocol
| Step | Action | Dilution | Volume |
|---|---|---|---|
| Initial suspension | Add 10 g (or 10 mL) of test sample to 90 mL MRD in Stomacher bag or blender jar. Homogenise 30–60s (Stomacher) or blend | 10⁻¹ (1:10) | 90 mL MRD + 10g sample |
| Rest | Allow 10–15 min at room temperature for injured cells to recover before further dilution | 10⁻¹ | — |
| First decimal dilution | Transfer 1 mL from 10⁻¹ into 9 mL MRD. Mix thoroughly (vortex 5s) | 10⁻² (1:100) | 9 mL MRD tube |
| Further dilutions | Repeat 1 mL → 9 mL transfers using fresh MRD tubes each step | 10⁻³, 10⁻⁴… | 9 mL MRD tubes |
| Plating | Inoculate agar plates from appropriate dilutions within 45 min | Per method SOP | Typically 1 mL or 0.1 mL |
QC Performance — Recovery Test
| Organism (ATCC) | Inoculum | Recovery Specification | Method |
|---|---|---|---|
| Staphylococcus aureus (6538) | 1,000–10,000 CFU/tube | ≥70% recovery vs control at T0, 45 min, 1h (35°C on TSA) | ISO 11133:2014/Amd 1:2018 |
| Pseudomonas aeruginosa (9027) | 1,000–10,000 CFU/tube | ≥70% recovery vs control at T0, 45 min, 1h | ISO 11133:2014/Amd 1:2018 |
| Escherichia coli (8739) | 1,000–10,000 CFU/tube | ≥70% recovery vs control at T0, 45 min, 1h | ISO 11133:2014/Amd 1:2018 |
| Candida albicans (10231) | 1,000–10,000 CFU/tube | ≥70% recovery vs control at T0, 45 min, 1h (on SDA) | ISO 11133:2014/Amd 1:2018 |
Literature & References
| # | Reference |
|---|---|
| 1 | ISO 6887-1:2017. Microbiology of the food chain — Preparation of test samples, initial suspension and decimal dilutions for microbiological examination — Part 1: General rules for preparation of initial suspension and decimal dilutions. Geneva: ISO; 2017. [Primary reference — MRD specified as standard diluent] |
| 2 | ISO 6887-4:2017. Part 4: Specific rules for the preparation of dairy products and dairy processing environment. Geneva: ISO; 2017. |
| 3 | ISO 11133:2014/Amd 1:2018. Performance testing of culture media — Amendment 1: Diluent performance testing. Geneva: ISO; 2018. [Recovery testing protocol for MRD] |
| 4 | Merck KGaA. Maximum Recovery Diluent, Cat. 0120635. Technical Data Sheet; current edition. [Reference commercial specification] |
| 5 | Oxoid. Maximum Recovery Diluent, Cat. CM0989. Technical information; current edition. |
📄 Full 16-section GHS SDS available (Australian WHS Regulations 2023 / GHS 7th Edition) — support@ausamics.com.au
Section 1 — Identification
| Product Name | Maximum Recovery Diluent (MRD) |
| Catalogue No. | AS-1411 |
| Intended Use | Isotonic diluent for food, dairy, environmental, and pharmaceutical microbiology — serial dilution and sample preparation per ISO 6887 |
| Supplier | AuSaMicS Pty Ltd | ABN 56 676 640 467 |
| Address | 31 Longview CT, Thomastown VIC 3074, Australia |
| Emergency | Poisons Information Centre: 13 11 26 (24 hr) |
| Phone | +61 412 520 598 | support@ausamics.com.au |
Section 2 — Hazard Identification (GHS 7th Ed / WHS 2023)
| GHS Classification | NOT classified as a hazardous substance under Australian WHS Regulations 2023 at intended use concentrations. |
| Signal Word | None required |
| Other Hazards | Combustible dry powder. Dust from NaCl and Tryptone may cause mild respiratory irritation — use P1 filter when weighing bulk quantities. No significant chemical hazard at laboratory handling levels. |
Composition Summary
| Component | g/L | CAS | Hazard |
|---|---|---|---|
| Tryptone (Pancreatic Digest of Casein) | 1.0 | 91079-38-8 | Not hazardous |
| Sodium Chloride (NaCl) | 8.5 | 7647-14-5 | Not hazardous at use level |
| Respiratory PPE | P1 filter when weighing bulk powder. Not required for routine small-scale handling. |
| Eye Protection | Safety glasses when handling dry powder |
| Skin / Gloves | Nitrile gloves when handling inoculated diluent and samples |
| First Aid — Eyes | Irrigate with water ≥10 min. Seek advice if irritation persists. |
| Waste (sterile / unused) | Dispose as general laboratory waste per local regulations. |
| Waste (inoculated samples) | Autoclave (121°C / 15 min) before disposal as microbiological waste per institutional biosafety procedures. |
| Transport | Not dangerous goods — ADG, IMDG, IATA |
| Regulatory | Australian WHS Regulations 2023 | GHS 7th Edition | AICIS compliant |
Quality Specifications
| Parameter | Specification | Method |
|---|---|---|
| Appearance (powder) | Cream to light beige, free-flowing, homogeneous powder | Visual |
| Appearance (prepared solution) | Clear, colourless to very pale straw; no precipitate or turbidity | Visual after dissolution |
| pH (prepared, 25°C) | 7.0 ± 0.2 | pH meter (calibrated) |
| Dissolution | Complete at 9.5 g/L; no undissolved particulate | Visual |
| Sterility | No growth after incubation at 35°C for 14 days (uninoculated tubes) | Sterility check per ISO 11133 |
| Recovery — S. aureus ATCC 6538 | ≥70% recovery vs T0 at T45 min and T1h at 35°C on TSA | ISO 11133:2014/Amd 1:2018 |
| Recovery — E. coli ATCC 8739 | ≥70% recovery vs T0 at T45 min and T1h | ISO 11133:2014/Amd 1:2018 |
| Recovery — P. aeruginosa ATCC 9027 | ≥70% recovery vs T0 at T45 min and T1h | ISO 11133:2014/Amd 1:2018 |
| Recovery — C. albicans ATCC 10231 | ≥70% recovery vs T0 at T45 min and T1h on SDA | ISO 11133:2014/Amd 1:2018 |
| Batch COA | Available every production lot | Included with every order |
Manufacturing & Documentation
Manufactured by AuSaMicS Pty Ltd
31 Longview CT, Thomastown VIC 3074, Australia | ABN 56 676 640 467
✓ Formulated per ISO 6887 specification — Tryptone 1.0 g/L + NaCl 8.5 g/L, pH 7.0 ± 0.2
✓ Equivalent to Merck/Millipore 0120635, Oxoid CM0989, BD Difco 218971
✓ Batch QC per ISO 11133:2014/Amd 1:2018 — pH, sterility, recovery performance
✓ COA, TDS, SDS included with every order
✓ Australian stock — same-week dispatch, no import delays
31 Longview CT, Thomastown VIC 3074, Australia | ABN 56 676 640 467
✓ Formulated per ISO 6887 specification — Tryptone 1.0 g/L + NaCl 8.5 g/L, pH 7.0 ± 0.2
✓ Equivalent to Merck/Millipore 0120635, Oxoid CM0989, BD Difco 218971
✓ Batch QC per ISO 11133:2014/Amd 1:2018 — pH, sterility, recovery performance
✓ COA, TDS, SDS included with every order
✓ Australian stock — same-week dispatch, no import delays
⚠️ For laboratory, food safety, dairy, environmental, and quality control use only. Not for food, therapeutic, or direct human use. Always autoclave inoculated diluent before disposal.