Dehydrated culture media
Standard Methods Agar (PCA) ISO/APHA
For the total plate count of aerobic microorganisms.
- Cat. No.
- LC-1056
- Category
- Dehydrated culture media
- Format
- 500 g
- Storage
- 2 to 25 °C
- Minimum guaranteed shelf life
- 15 months
- Standards
- APHAISO 11133ISO 4833
- Also available
- Ready-to-use medium, 4 formats (LC-903)
Standard Methods Agar (PCA) is recommended by APHA for the counting of bacteria of sanitary interest, which are indicators of contamination or microbial load in foods.
Key features
Applications
Non-selective enumeration of aerobes.
Industry
Dairy products, food.
Standards
APHA, ISO 11133, ISO 4833.
Preparation
23.5 g in one liter of distilled water; boil for one minute, sterilize in autoclave at 121 °C for 15 minutes.
Principles and uses
Enzymatic digest of casein provides nitrogen, vitamins, minerals and amino acids essential for growth. Yeast extract is source of vitamins, particularly the B-group. Dextrose is the fermentable carbohydrate providing carbon and energy. Bacteriological agar is the solidifying agent.
This medium is recommended by ISO 4833 for the colony count technique of microorganisms at 30 °C in the food chain.
Technical specifications
| Solubility | Without residues |
|---|---|
| Appearance | Fine powder |
| Color of the dehydrated medium | Light toasted |
| Color of the prepared medium | Amber, slightly opalescent |
| Final pH (25 °C) | 7.0 ± 0.2 |
| Amount per litre | 23.5 g |
| Storage | 2 to 25 °C |
Formula
| Ingredient | g/L |
|---|---|
| Enzymatic digest of casein | 5 |
| Bacteriological agar | 15 |
| Glucose anhydrous | 1 |
| Yeast extract | 2.5 |
Preparation and use
Preparation
Suspend 23.5 grams of the medium in one liter of distilled water. Mix well and dissolve by heating with frequent agitation. Boil for one minute until complete dissolution. Sterilize in autoclave at 121 °C for 15 minutes. Cool to 44-47 °C and dispense into appropriate containers.
Instructions for use
For the colony count at 30 °C according to ISO 4833:
Pour plate technique:
- Inoculate 1 mL of the sample (if necessary 2 continuous decimal dilutions to be able to count between 15-300 colonies per plate).
- Put 12-15 mL per plate of agar cooled to 44-47 °C in each Petri dish. The time of preparation should not exceed 45 minutes.
- Invert the plates and incubate at 30 ± 1 °C for 72 ± 3 hours.
- Post incubation, count the colonies.
Surface plating technique:
- Inoculate 0.1 mL of the sample (if necessary 2 continuous decimal dilutions to be able to count between 15-300 colonies per plate).
- Spread the inoculum on the surface of the agar plate.
- Leave the plates with the caps on for 15 minutes to allow the inoculum to be absorbed into the agar.
- Invert the plates and incubate at 30 ± 1 °C for 72 ± 3 hours.
- After the incubation, count the colonies.
According to APHA, incubate the Petri dishes at 32 ± 2 °C for 18-48 hours and count the developed colonies. Consult the specific texts of APHA for the particular sample applications.
Quality control
According to ISO 11133
Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 6538 and Bacillus subtilis ATCC 6633.
Incubation conditions: 30 ± 1 °C / 72 ± 3 h.
Inoculation conditions: productivity quantitative (100 ± 20 CFU, min. 50 CFU).
Reference media: TSA.
According to APHA
Escherichia coli ATCC 8739, Staphylococcus aureus ATCC 25923 and Staphylococcus epidermidis ATCC 12228.
Incubation conditions: 32 ± 2 °C / 18-48 h.
| Microorganism | Specification |
|---|---|
| Staphylococcus epidermidisATCC 12228 | Good growth |
| Staphylococcus aureusATCC 25923 | Good growth |
| Staphylococcus aureusATCC 6538 | Good growth > 70% |
| Bacillus subtilisATCC 6633 | Good growth > 70% |
| Escherichia coliATCC 8739 | Good growth > 70% |
Bibliography
- International Standard ISO 4833 Microbiology of food and animal feeding stuffs - Horizontal method for the enumeration of microorganisms - Colony-count technique at 30 °C
- Standard Methods for the Examination of Dairy Products, 13th Ed. APHA, 1972. American Public Health Association.
- Recommended Methods for the Microbiological Examination of Foods, APHA Inc. New York, 1958.
- Standard Methods for the Examination of Water and Wastewater, APHA Inc. New York, 1960.
APHA: American Public Health Association Inc.
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