Lactose Monohydrate Sulphite Medium (Medium R)

Composition**

Final pH (at 25°C): 7.1±0.1

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 19.8 grams of dehydrated medium in 1000 ml purified/ distilled water. Heat if necessary to dissolve in tubes containing inverted Durham's tubes. Sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to 45-50°C and add filter-sterilized solution of 1.2% sodium metabisulphite R (0.5ml) and 1.0% ferric ammonium citrate (0.5ml) to each tube.

Principle And Interpretation

Lactose Monohydrate Sulphite Medium base is prepared as per the British Pharmacopoeia (1) and is cited as Medium R. This medium is useful in semi-quantitative test for presence of Clostridium perfringens in pharmaceutical products where the level of this species is a criterion of quality.

The medium contains pancreatic digest of casein and yeast extract, which provides essential nitrogenous compounds for Clostridia. Lactose monohydrate serves as carbon or fermentable carbohydrate source. Cystine hydrochloride rich in sulphur content provides reduced conditions. Sodium metabisulphite and ferric ammonium citrate act as indicators of sulphite reduction, indicated by blackening of the medium.

Quality Control

Appearance: Cream to yellow homogeneous free flowing powder

Colour and Clarity of prepared medium: Light amber coloured clear solution without any precipitate

pH: 7.00-7.20

Growth Promotion Test: Growth Promotion is carried out in accordance with British pharmacopoeia

Cultural Response

M1287B: Cultural characteristics after an incubation at 46±0.5°C for 24-48 hours.

Storage and Shelf Life

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

Reference

1. British Pharmacopoeia, 2009, The Stationery office British Pharmacopoeia.