ISP Medium No. 7 (Tyrosine Agar)

Intended Use

Recommended for isolation and characterization of Streptomyces species as per International Streptomyces Project.

Composition**

Final pH ( at 25°C): 7.3±0.1

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 23.74 grams (the equivalent weight of dehydrated medium per litre) in 1000 ml purified/distilled water containing 15 ml glycerol. 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

Streptomyces and Nocardia species appear morphological similar in clinical material and in culture (3,4). Nocardiosis, caused by Nocardia species, is a disease of man, most frequently encountered in patients who are severely immunosuppressed and in animals (3). Streptomyces species may be differentiated from Nocardia species based on tyrosine and asparagine utilization. Clear zones in the medium surrounding colony growth indicate hydrolysis of the substrate present (3,4). International Streptomyces Project Medium No. 7 (Tyrosine Agar) is recommended for the isolation and enumeration of Streptomyces species (1). It is used for the differentiation of Streptomyces species based on tyrosine utilization.

The medium contains L-tyrosine, which is utilized by Streptomyces species. Zone of clearance around the colony indicates tyrosine hydrolysis. Trace elements provide essential factors for the growth of Streptomyces species. Inoculate the medium by streaking the isolate to be tested onto the agar surface with a sterile inoculating loop. The medium may need to be incubated for upto 3 weeks to allow positive hydrolytic reactions to develop. Examine plates at regular intervals for growth and hydrolysis.

Type of specimen

Food samples

Specimen Collection and Handling

For food samples, follow appropriate techniques for sample collection and processing as per guidelines (5). 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. Further biochemical tests must be carried out for confirmation.

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 2.0% agar gel.

Colour and Clarity of prepared medium: Yellow coloured, clear to slightly opalescent gel forms in Petri plates

Reaction: Reaction of 2.37% w/v aqueous solution containing 1.5% glycerol at 25°C. pH : 7.3±0.1

pH: 7.20-7.40

Cultural Response: Cultural characteristics observed after an incubation at 25-30°C for 48-72 hours.(Tyrosine hydrolysis is observed upto 3 weeks)

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 (2,3).

Reference

1. Atlas R. M., 1993, Handbook of Microbiological Media, 3rd ed., CRC Press. Inc.
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. Larone, 1995, Medically Important Fungi: A Guide to Identification, 3rd Ed., American society for Microbiology, Washington, D.C.
5. Salfinger Y., and Tortorello M.L. Fifth (Ed.), 2015, Compendium of Methods for the Microbiological Examination of Foods, American Public Health Association, Washington, D.C.