Crossley SM Medium

Intended Use

Recommended for examination of meat and meat products for sporing anaerobes.

Composition**

Final pH (at 25°C): 6.8±0.2

**Formula adjusted, standardized to suit performance parameters

# Equivalent to Skim milk powder

Directions

Suspend 110.1 grams in 100 ml purified / distilled water, agitating continuously. Mix well and make up the volume to 1000 ml. Dispense into tubes or flasks as desired. Sterilize by autoclaving at 15 lbs pressure (121°C) for 5 minutes.

Principle And Interpretation

SM powder contains the carbohydrate lactose along with three main proteins i.e. casein, lactalbumin and lactoglobulin (1). Therefore an organism may exhibit one or several of the following metabolic properties, each specific for a particular species aiding bacterial identification. The various metabolic functions are lactose fermentation, clot formation, peptonization (digestion) and gas formation (5).

This medium was originally described by Crossley for the examination of meat and meat products for the detection of anaerobic bacteria (2). 10 ml of the medium is inoculated with 1-2 grams of food sample. The tubes are incubated at 35-37°C for 3-4 days. Peptone serves as a source of carbonaceous and nitrogeneous compounds, long chain amino acids, vitamins and other essential nutrients. Bromo cresol purple is the pH indicator. The reaction are observed at regular intervals to determine the change.

Type of specimen

Meat and meat products

Specimen Collection and Handling

For meat and meat products, 10 ml of the medium is inoculated with 1-2 grams of food sample. The tubes are incubated at 35-37°C for 3-4 days. The reaction are observed at regular intervals to determine the change.

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. Some strains may show poor growth due to nutritional variations.
2. Further biochemical and serological testing may be required for complete identification.

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 Light yellow to pale blue homogeneous free flowing powder.

Colour and Clarity of prepared medium Pale blue coloured opaque milky solution

Reaction Reaction of 11.0% w/v aqueous solution at 25°C. pH : 6.8±0.2

pH 6.60-7.00

Cultural Response Cultural characteristics observed after an incubation at 35-37°C for upto 3-5 days and record the reactions of various intervals during the incubation.

Key : (*) Corresponding WDCM numbers.

Storage and Shelf Life

Store between 10-30°C in a tightly closed container and the prepared medium at 2-8°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. Use before expiry date on the label.

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 (8,9).

Reference

1. Cantarow A., Schepartz B., Biochemistry, 3rd Ed., Philadelphia: W B Saunders, 1962:273,792-793
2. Crossley E.L. (1941) J. Soc. Chem. Ind. 60 131-136
3. Isenberg, H.D. Clinical Microbiology Procedures Handbook 2nd Edition.
4. 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.
5. MacFaddin J. F., 2000, Biochemical tests for Identification of Medical Bacteria, 3rd Ed., Lippincott, Williams and Wilkins, Baltimore.