Description
Amyl Phenol Red Broth Base AM 726 containing the required fermentable carbohydrate is used for identification studies on a wide range of bacteria. The carbohydrate free basal medium is capable of supporting the growth of fastidious and less fastidious organisms and, when supplemented with the required carbohydrate, those organisms capable of utilising that carbohydrate will produce acid or acid and gas, thereby altering the pH of the medium and causing a colour change as the Phenol Red indicator changes from red to yellow. Phenol Red indicator changes to yellow at pH 6.8 and is red at pH 7.4 and, for this reason, is particularly suitable for detecting the small changes in pH which is characteristic of fermentation by nutritionally exacting bacteria. Although a number of carbohydrates are capable of withstanding normal heat sterilization temperatures, many may have their structure altered by these procedures and, therefore, it is preferable that a filter sterilised solution of the carbohydrate is added to the sterilised, cooled basal medium and aseptically distributed as outlined in preparation procedure.
If very fastidious organisms such as suspected Neisseria sp. or Streptococcus pneumoniae are to be inoculated into the medium, a small amount of sterile rabbit or bovine serum, usually 5 %, can be added prior to dispensing into inoculation tubes. Cultivation of anaerobic organisms can be enhanced by the addition of a small amount of agar e.g. 0.5-0.1% , prior to sterilising the basal medium and, just before inoculating the suspected anaerobe, the medium is heated to boiling so as to drive off dissolved oxygen, and cooled to below 40°C. 1,2
