Plate Count Agar (Standard Methods Agar)
Intended use
Recommended for the determination of plate counts of microorganisms in food, water, waste water samples.
Composition**
Ingredients Gms / Litre
Tryptone 5.000
Yeast extract 2.500
Dextrose (Glucose) 1.000
Agar 15.000
Final pH ( at 25°C) 7.0±0.2
Directions
Suspend 23.5 grams in 1000 ml purified/distilled water. Heat to boiling to dissolve the medium completely. Sterilize by
autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 45-50°C. Mix well and pour into sterile Petri plates.
Principle And Interpretation
Plate Count Agar is formulated as described by Buchbinder et al (1) which is recommended by APHA (2,3,4) and FDA (5).
Tryptone provides nitrogenous and carbonaceous compounds, long chain amino acids, and other essential nutrients. Yeast
extract supplies Vitamin B complex. APHA recommends the use of pour plate technique. The samples are diluted and
appropriate dilutions are added in Petri plates. Sterile molten agar is added to these plates and plates are rotated gently to
ensure uniform mixing of the sample with agar. The poured plate count method is preferred to the surface inoculation
method, since it gives higher results. Plate Count Agar is also suitable for enumerating bacterial count of sterile rooms.
Type of specimen
Food and dairy samples; Water samples
Specimen Collection and Handling:
For food and dairy samples, follow appropriate techniques for sample collection and processing as per guidelines (3,4). For
water samples, follow appropriate techniques for sample collection, processing as per guidelines and local standards (2).
After use, contaminated materials must be sterilized by autoclaving before discarding.
Warning and Precautions :
Read the label before opening the container. Wear protective gloves/protective clothing/eye protection/ face protection. Follow good microbiological lab practices while handling specimens and culture. Standard precautions as per established guidelines should be followed while handling specimens. Safety guidelines may be referred in individual safety data sheets.
Limitations :
1. Individual organisms differ in their growth requirement and may show variable growth patterns on the medium.
2. Each lot of the medium has been tested for the organisms specified on the COA. It is recommended to users to validate the medium for any specific microorganism other than mentioned in the COA based on the user’s unique requirement.
Performance and Evaluation
Performance of the medium is expected when used as per the direction on the label within the expiry period when stored at
recommended temperature.
Quality Control
Appearance
Cream to yellow homogeneous free flowing powder
Gelling
Firm, comparable with 1.5% Agar gel
Colour and Clarity of prepared medium
Light yellow coloured clear to slightly opalescent gel forms in Petri plates
Reaction
Reaction of 2.35% w/v aqueous solution at 25°C. pH : 7.0±0.2
pH: 6.80-7.20
Cultural Response
Cultural characteristics observed after an incubation at 35 - 37°C for 18 - 48 hours
Storage and Shelf Life
Store between 10-30°C in a tightly closed container and the prepared medium at 20-30°C. Use before expiry date
on the label. On opening, product should be properly stored dry, after tightly capping the bottle inorder to prevent
lump formation due to the hygroscopic nature of the product. Improper storage of the product may lead to
lump formation. Store in dry ventilated area protected from extremes of temperature and sources of ignition
Seal the container tightly after use. Product performance is best if used within stated expiry period.
Disposal
User must ensure safe disposal by autoclaving and/or incineration of used or unusable preparations of this product. Follow
established laboratory procedures in disposing of infectious materials and material that comes into contact with sample must be decontaminated and disposed of in accordance with current laboratory techniques.
