Determination of phenol coefficient (Rideal walker coefficient) of a given disinfectant or antimicrobial agent.

Phenol coefficient may be defined as the killing power of germicide or an antimicrobial agent towards a test organism compared to that of phenol under identical conditions. It is the ratio of the higher dilation of disinfectant killing the organism in 10min. but not in 5min, to the of the highest dilution of phenol showing the same result.
Materials: – 24 hrs. Broth culture of S.aureus
Sterile test tube (10)
Platinum 100p
Nutrient broth (10ml per tube)
Distilled water.
Sterile diln flask.
Sterile 5 and 10ml graduated pipettes.
Various dilution of phenol.
Various dilution of disinfectant under test.
Place 5ml of various dilutions of phenol and disinfectant under test into sterile test tube Label them from 1 to 10, place 0.5ml of broth culture of test organism into tubes no1, shake to distribute the organism and at 30sec. internal thereafter add 0.5ml of culture of test organism in to tubes no1, shake to distribute the organism and at 30 sec. interval thereafter add 0.5ml of culture to the remaining tubes containing various dilutions. When tube no.10 is inoculated 41/2 min will be passed 30 second later proceeding as follows.
Place one standard loopful from tube no1 to the tube of broth and at 30sec. internal thereafter transfer a loopful of each successive disinfecting mix. This will give 3 series of inoculation to a fresh tube of broth until 3 transfers have been made from each disinfecting mix. This will give 3 series of inoculation in to broth after 5,10 and 15 min exposure of test organisms, through various concentrations. of disinfectant. In cubit broth tubes at 370c for 48hrs. Record in a tubular from presence or absence of growth.

Various dilutions of phenol are done on follows shown in picture to determine Phenol coefficient

Interpretation of results for phenol coefficient

calculation of phenol coefficient

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