Nutrient Broth, AOAC

Nutrient Broth, AOAC is used as a culture growth medium for testing disinfectants in accordance with AOAC, 2000. (under Disinfectants Subchapter 1, Phenol coefficient methods).

Composition**

Final pH ( at 25°C): 6.8±0.2

**Formula adjusted, standardized to suit performance parameters

Directions

Suspend 20 grams in 1000 ml distilled water. Heat if necessary to dissolve the medium completely. Dispense 10 ml portions in 20 x 150 mm test tubes and sterilize by autoclaving at 15 lbs pressure (121°C) for 20 minutes.

Principle And Interpretation

Nutrient broth AOAC is an equivalent medium recommended by AOAC for testing disinfectants i.e phenol against Salmonella Typhi. Peptic digest of animal tissue and beef extract provides necessary nutrient sources for growth of Salmonella. Sodium chloride helps to maintain osmotic balance. If colorimetric method is used, adjust broth to give dark green with bromothymol blue. The recommended test organism used to study phenol coefficient is S.Typhi ATCC 6539. The stock culture which is maintained on nutrient agar slants is inoculated in this medium and consecutive transfers are made.

Before using culture for testing, it is incubated at 37°C. A 22-26 hour culture of organism is grown in Nutrient broth, AOAC (M1680) and incubated at 35-37°C, which is used in test. Shake and let settle 15 min before using. Phenol coefficient method is further carried out as described in AOAC (1).

Quality Control

Appearance: Cream to yellow homogeneous free flowing powder

Colour and Clarity of Prepared medium: Light amber coloured, clear solution in tubes

Reaction: Reaction of 2.0% 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 18-48 hours.

Storage and Shelf Life

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

Reference

1. Official Methods of Analysis AOAC International , 2000 17th edition, Volume 1. Edited by Dr. Horwitz,W. Published by AOAC International.USA..Chapter 6. Disinfectants Subchapter 1. Phenol coefficient methods AOAC official methods 955.1