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Laboratory Preparations/Biological Extracts

RINGER SOLUTION 1/4 STRENGTH RINGERS SOLUTION TABLETS

Code: BR0052

Formula

gm/litre

Sodium chloride

2.25

Potassium chloride

0.105

Calcium chloride 6H2O

0.12

Sodium bicarbonate 0.05

0.05

pH*

 

One tablet makes 500 ml of quarter-strength Ringers solution.

*Due to the low ionic strength of this medium the pH is not specified.

Directions
To prepare quarter-strength Ringers Solution, dissolve 1 tablet in 500ml of distilled water. Sterilise by autoclaving at 121°C for 15 minutes.

Description
These tablets are prepared according to the formula in the Dept. of Health & Social Security publication Memo. 139/ Foods1. They dissolve readily in water to give a solution which does not precipitate when sterilised by autoclaving. The sterile solution is used as an isotonic diluent for both bacterial cells and bacteriological specimens, or as a rinse during the bacteriological examination of plant and apparatus.

Also see:
BR0048 Thiosulphate Ringers Tablets
BR0049 Calgon Ringers Tablets

Quality control testing of 1/4 Strength Ringers Solution Tablets includes testing as a diluent in accordance with ISO 11133:20142.

Technique
Oxoid quarter-strength Ringers Solution may be used for the decimal dilution of milk and dairy product samples, e.g. prior to inoculation into MacConkey Broth for the presumptive coliform test, the maceration and suspension of solid food and other specimens before bacteriological examination; the preparation of suspensions and serial dilutions from pure cultures of bacteria; the examination of dairy plant and apparatus by the swab or rinse method3.

Quality Control
A satisfactory result is represented by recovery of ± 30% of the control number of colony forming units (CFU) taken at time 0 from an inoculum of 50 cfu to 150 cfu after holding at 20 °C to 25 °C for 45 minutes to 60 minutes.

Positive controls:

Expected results

Escherichia coli ATCC® 25922*
WDCM00013

White/grey colonies on the control medium Tryptone Soya Agar

Staphylococcus aureus® ATCC 25923*
WDCM00034

White/grey colonies on the control medium Tryptone Soya Agar

Negative Control:

 

Uninoculated medium

No change


*organism available as a Culti-Loop™

References
1.
Dept. of Health & Social Security (1937) Memo. 139/Foods.
2. International Organization for Standardization. ISO 11133:2014 Microbiology of food, animal feed and water - Preparation, production, storage and performance testing of culture media
3. Davis J. G. (1956) `Laboratory Control of Dairy Plant’. Dairy lndustries Ltd., London.

 
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