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Phenol coefficient test is best known screening test in which potency of a disinfactant is compared with that of phenol. A series of a dilutions of phenol and the disinfactant being tested are prepared. A standard amount of Salmonella tyhpii and Staphylococcus aureus are added to each dilution; the dilutions are then placed in a 20 to 37oC water bath. At 5-minute intervas, samples are withdrawn from each dilution and used to inoculate a growth medium, which is incubated for two or more days and then examined the growth. If there is no growth in the growth medium, the dilution at that particular time of sampling killed the bacteria. The highest dilution that kills the bacteria after 1o min. expousre, but not at 5min. is used to calculate the phenol coefficient. This is done by dividing the resiprocal of the appropriate phenol dilution.
