Saline Peptone Water ISO (Maximum Recovery Diluent) MRD

ISO 6887 recommends this medium as a diluent for the preparation of the initial suspension for microbiological samples. The low concentration of peptone does not cause a multiplication of the organisms within 1-2 hours of dilution of the sample. It is also used for carbohydrate fermentation tests in many food and environment studies, amongst others. To determine carbohydrate fermentation patterns, add 1.8 mL of 1% phenol red to reconstitute the dry medium. After dispensing into test tubes with Durham gas collecting vials for gas detection, sterilize at 121 °C for 15 minutes. Aseptically add sterile carbohydrate solution (dextrose) to yield 1% final concentration.

Peptone is the nutrient source of nitrogen, vitamins, amino acids and minerals. Sodium chloride maintains the osmotic balance.

Preparation

Suspend 9.5 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. Dispense into appropriate containers and sterilize in autoclave at 121 °C for 15 minutes.

Instructions for use

1. Refer to the relevant references for details on test methods.
2. Inoculate the tubes with the test sample.
3. Incubate the tubes at 35 ± 2 °C for 18-24 hours under aerobic conditions, or as indicated in the references.

• Coccolin L., Manzano M., Cantur C., Comi G. App. Environ. Microbiol. 2001 Nov. 67 (11) 5113-21.
• Destoumieux-Garzon D., Saulnier D., Garnier et al. J. Biol. Chem. Vol. 276. Issue 50, 47070-47077 (14 December 2001).
• ISO 6887 Microbiology - General guidance for the preparation of dilutions for microbiological examinations.