Plate Count Skim Milk Agar (PCSM)
Overview
Plate Count Skim Milk Agar (PCSMA) is the international reference solid medium for the enumeration of total aerobic mesophilic microorganisms in milk, cream, whey, butter, cheese, ice cream, and other dairy products.
It is the mandatory medium specified in ISO 4833-1:2013 (pour-plate technique) and IDF Standard 100B:1991 when milk solids are required for optimal recovery of injured dairy organisms. The inclusion of 10% skimmed milk powder provides natural growth factors, casein, lactose, and vitamins that significantly enhance recovery of heat-stressed and freeze-stressed cells compared to standard Plate Count Agar (PCA).
Intended Use / Applications
- Total viable aerobic count (TVC/TAC) in raw milk, pasteurised milk, UHT milk, milk powder, and fermented milks
- Official method — ISO 4833-1:2013 pour-plate technique
- Reference method — IDF Standard 100B:1991 / FIL/IDF
- Preferred over standard PCA for superior recovery of stressed dairy flora
- Enumeration in cream, whey, butter, cheese, and ice cream
Key Features
- Skim-milk powder (10%) — supplies natural growth factors, casein, lactose, and vitamins
- Significantly higher colony counts than standard PCA for stressed dairy organisms
- Transparent medium — facilitates precise, unambiguous colony counting
- Compliant with ISO 4833-1:2013 and IDF Standard 100B:1991
Composition (per litre)
| Ingredient | Amount | Unit |
|---|---|---|
| Tryptone (Pancreatic Digest of Casein) | 5.0 | g |
| Yeast Extract | 2.5 | g |
| Glucose (Dextrose) | 1.0 | g |
| Skimmed Milk Powder (heat-treated) | 100.0 | g |
| Agar | 12.0–15.0 | g |
Final pH: 7.0 ± 0.2 at 25 °C
Official References
ISO 4833-1:2013 IDF 100B:1991 FIL/IDF
Storage
| Dehydrated Medium | 10–30 °C, dry place, away from light; keep container tightly sealed |
| Prepared Plates | 2–8 °C, sealed, use within 4 weeks |
| Scope | For dairy microbiology laboratory use only |
Product Specifications
| Product Name | Plate Count Skim Milk Agar |
| Catalogue Number | AS-1329 |
| Format | Dehydrated granular medium |
| Appearance | Cream to light beige homogeneous powder |
| Final pH (25 °C) | 7.0 ± 0.2 |
| Gel Strength | Firm, transparent gel after autoclaving |
| Sterility | Sterile upon preparation per protocol |
Composition (per litre)
| Ingredient | g/L | Function |
|---|---|---|
| Tryptone (Pancreatic Digest of Casein) | 5.0 | Nitrogen source |
| Yeast Extract | 2.5 | Growth factors, vitamins |
| Glucose (Dextrose) | 1.0 | Fermentable carbon source |
| Skimmed Milk Powder (heat-treated) | 100.0 | Casein, lactose, vitamins, growth stimulants |
| Agar | 12.0–15.0 | Solidifying agent |
Preparation Instructions
- Suspend all components (tryptone, yeast extract, glucose, skimmed milk powder, agar) in 1 litre of purified water.
- Mix thoroughly. Note: milk powder dissolves slowly — allow sufficient time with constant agitation.
- Heat with frequent agitation and bring to a boil for 1–2 minutes until completely dissolved.
- Autoclave at 121 °C for 15 minutes. Do not over-autoclave; excessive heat degrades milk proteins.
- Cool to 45–50 °C in a water bath before dispensing.
- Pour 20–25 mL per sterile 90 mm Petri dish on a level surface. Allow to solidify.
- Store prepared plates at 2–8 °C in sealed bags for up to 4 weeks.
Incubation Conditions
| Standard — ISO 4833-1 | 30 ± 1 °C for 72 ± 3 hours (pour-plate technique) |
| Alternative (national methods) | 35 ± 1 °C for 48 hours |
| Technique | Pour-plate as specified in ISO 4833-1:2013 |
Quality Control
| Test Organism | ATCC / NCTC | Expected Result |
|---|---|---|
| Escherichia coli | ATCC 25922 | Good growth; cream colonies |
| Staphylococcus aureus | ATCC 25923 | Good growth; golden colonies |
| Lactobacillus acidophilus | ATCC 4356 | Good growth; small white colonies |
Section 1 — Identification
| Product Name | Plate Count Skim Milk Agar |
| Catalogue Number | AS-1329 |
| Supplier | AuSaMicS Pty Ltd, 31 Longview CT, Thomastown, VIC 3074, Australia |
| Phone | +61 412 520 598 |
| support@ausamics.com.au | |
| Emergency | Poisons Information Centre: 13 11 26 (Australia) |
| Recommended Use | Microbiological culture medium — laboratory use only |
Section 2 — Hazard Identification
GHS Classification: Not classified as a hazardous substance under GHS criteria when used as directed.
Signal Word: None required.
Precautionary Statements: P261 — Avoid breathing dust. P280 — Wear protective gloves/eye protection. P501 — Dispose of contents/container per local regulations.
Other Hazards: Inoculated material may harbour live microorganisms. Handle per institutional biosafety guidelines.
Section 3 — Composition
| Ingredient | CAS Number | % w/w | GHS Hazard |
|---|---|---|---|
| Tryptone | Mixture | ~0.5 | Not classified |
| Yeast Extract | 8013-01-2 | ~0.2 | Not classified |
| Glucose (Dextrose) | 50-99-7 | ~0.1 | Not classified |
| Skimmed Milk Powder | Mixture | ~9.1 | Not classified |
| Agar | 9002-18-0 | ~1.1–1.4 | Not classified |
Section 4 — First Aid
Inhalation: Remove to fresh air. Seek medical attention if symptoms persist.
Skin Contact: Wash with soap and water. Seek medical attention if irritation develops.
Eye Contact: Flush with water for at least 15 minutes. Seek medical attention if irritation persists.
Ingestion: Do not induce vomiting. Rinse mouth with water. Seek medical attention if unwell.
Section 7 — Handling and Storage
Handling: Use good laboratory practices. Wear appropriate PPE. Avoid breathing dust. Wash hands after handling.
Storage: Dehydrated medium — 10–30 °C, dry, away from light, container tightly closed. Prepared plates — 2–8 °C, use within 4 weeks.
Section 13 — Disposal
Inoculated medium: Autoclave at 121 °C for 30 minutes before disposal. Dispose as biological waste per institutional biosafety procedures.
Dehydrated medium: Dispose per local regulations.
Section 14 — Transport
Not a dangerous good. Not regulated under ADG, IATA, or IMDG.
Section 15 — Regulatory
Not a scheduled poison (SUSMP). All components listed or exempt under AICS (Australian Inventory of Chemical Substances).
⬇ Download Full SDS — 16 Sections (PDF)Product Identification
| Product Name | Plate Count Skim Milk Agar |
| Catalogue Number | AS-1329 |
| Lot Number | XXXXXXXXX |
| Manufacture Date | XXXX-XX-XX |
| Expiry Date | XXXX-XX-XX |
| Format | Dehydrated granular medium |
Analytical Results
| Test Parameter | Specification | Result | Status |
|---|---|---|---|
| Appearance (powder) | Cream to light beige, homogeneous | Conforms | PASS |
| pH at 25 °C (prepared) | 7.0 ± 0.2 | X.X | PASS |
| Gel Strength | Firm, transparent gel | Conforms | PASS |
| Sterility (prepared) | No growth after 14 days | No growth | PASS |
| Growth — E. coli ATCC 25922 | Good growth; cream colonies | Conforms | PASS |
| Growth — S. aureus ATCC 25923 | Good growth; golden colonies | Conforms | PASS |
| Growth — L. acidophilus ATCC 4356 | Good growth; small white colonies | Conforms | PASS |
| Moisture Content | ≤ 5.0 % | X.X % | PASS |
✓ Overall Lot Status: RELEASED FOR USE
This lot meets all specified quality criteria and is released for use in accordance with AuSaMicS Pty Ltd quality management procedures.
Authorisation
| Authorised Signatory | Hassan Salimi |
| Title | Founder and Technical Director |
| Organisation | AuSaMicS Pty Ltd |
| Date of Issue | 2025-01-01 |
| Signature | _________________________________ |