Thiomersal Assay Medium

Thiomersal Assay Medium is recommended for microbiological assay of thiomersal as per I.P.

Composition**

Final pH ( at 25°C): 7.5±0.1

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 33.5 grams in 1000 ml distilled water. Heat to boiling to dissolve the medium completely. Sterilize by autoclaving at 15 lbs pressure (121°C) for 20 minutes. Mix well and pour in sterile Petri plates.

Principle And Interpretation

Thiomersal Assay Medium is used for microbiological assay of thiomersal using Micrococcus flavus as the test organism (1).

Test procedure : Growth of 18-24 hours old culture is emulsified in 10 ml of sterile normal saline. Add 1.5 ml of the inoculum to 150 ml of the medium cooled to 45-50°C. Mix well and pour into Petri plates to a depth of 3-4 mm. Cool the medium. The assay is carried out by cylinder plate or cup plate method, incubating the plates at 30°C for 18-24 hours (1).

Casein enzymic hydrolysate, beef extract and yeast extract provides nitrogenous and other essential growth nutrients. Sodium chloride maintains osmotic balance of the medium. Sucrose is the source of carbon.

Quality Control

Appearance: Cream to yellow homogeneous free flowing powder

Gelling: Firm, comparable with 1.5% Agar gel

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

Reaction: Reaction of 3.35% w/v aqueous solution at 25°C. pH : 7.5±0.1

pH: 7.40-7.60

Cultural Response

M1455: Cultural characteristics observed after an incubation at 30°C for 18 - 24 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. Indian pharmacopoeia, 2010, Ministry of Health and Family Welfare, Govt. of India.