APT Agar

Intended Use

Recommended for cultivation of heterofermentative Lactobacilli and other organisms requiring a high thiamine content.

Composition**

Final pH ( at 25°C): 6.7±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 61.18 grams in 1000 ml purified/distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15lbs pressure (121°C) for 15 minutes. AVOID EXCESSIVE HEATING. Cool to 45-50°C. Mix well and pour into sterile Petri plates or tubes or as desired.

Principle And Interpretation

APT (All purpose Tween 80) Agar is formulated as per Evans and Niven (1) for cultivation and maintenance of Lactobacilli. This medium is also used in the microbiological assay of thiamine. Lactobacillus forms a major part of lactic acid bacteria group which are abundant in nature. They convert lactose and other sugars to lactic acid and therefore are named as Lactobacillus. They are responsible for spoilage of foods like meat, dairy etc. However APT Agar can also be used for cultivation of heterofermentative lactic acid bacteria requiring high thiamine content (4). APT Agar is also used as a maintenance medium since it preserves the viability and sensitivity of Weissella viridescens ATCC12706 (formerly Lactobacillus viridescens).

APT Agar contains tryptone, which acts as a source of carbon, nitrogen, vitamins and minerals. Yeast extract provides vitamin and B-complex nutrients, which is required for the growth of bacteria. Dextrose is the carbohydrate source. Manganese chloride, magnesium sulphate and ferrous sulphate provide ions used in replication by lactobacilli. Polysorbate 80 is a source of fatty acids required by lactobacilli.

Type of specimen

Food samples- cured meat products, tinned foods, fruit juices.

Specimen Collection and Handling

For food samples, follow appropriate techniques for sample collection and processing as per guidelines (4). 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. It require a settling period before pH testing of the prepared medium. If the pH is tested immediately after preparation and is out of specification, retest the medium after 24 hours to obtain the specified pH.

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: Yellow coloured clear to slightly opalescent gel forms in Petri plates

Reaction: Reaction of 6.12% w/v aqueous solution at 25°C. pH : 6.7±0.2

pH: 6.50-6.90

Cultural Response

Cultural characteristics observed after an incubation at 35-37°C for 18-24 hours.

Key : (*) Corresponding WDCM numbers. (#) Formerly known as Lactobacillus viridescens

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 in order 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 (2,3).

References

1. Evans and Niven, 1951, J. Bact., 62:599.
2. Isenberg, H.D. Clinical Microbiology Procedures Handbook 2nd Edition.
3. Jorgensen, J.H., Pfaller, M.A., Carroll, K.C., Funke, G., Landry, M.L., Richter, S.S and Warnock., D.W. (2015) Manual of Clinical Microbiology, 11th Edition. Vol. 1.
4. Salfinger Y., and Tortorello M.L. Fifth (Ed.), 2015, Compendium of Methods for the Microbiological Examination of Foods, 5th Ed., American Public Health Association, Washington, D.C.