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Prof. Dr. Marlina, MS., Apt. PHENOL COEFFICIENT Phenol coefficient is a measure of the bactericidal activity of a chemical compound in relation to phenol. When listed numerically, the figure expressing the disinfecting power of a substance by relating it to the disinfecting power of phenol may be a function of the standardized test performed. Phenol coefficient test is best known screening test in which potency of a disinfectant is compared with that of phenol. A series of a dilutions of phenol and the disinfectant 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 At 5-minute intervals, samples are withdrawn from each dilution and used to inoculate a growth medium, which is incubated for two or more days and then examined the growth.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. exposure, but not at 5min. is used to calculate the phenol coefficient. This is done by dividing the reciprocal of the appropriate phenol dilution. For example, the Rideal-Walker method gives a Rideal- Walker coefficient and the U.S. Department of Agriculture method gives a U.S. Department of Agriculture coefficient. To calculate phenol coefficient ; the concentration of phenol at which the compound kills the test organism in 10 minutes, but not in 5 minutes, is divided by the concentration of the test compound that kills the organism under the same conditions (or, probably more common, dividing the dilution factor at which the tested substance shows activity by the dilution factor at which phenol shows comparable activity). The phenol coefficient may be determined in the presence of a standard amount of added organic matter or in its absence. A related way to express the bactericidal activity of an agent (at a given concentration) is by employing the formula : k = N/C·T where N is the number of surving cells, C is the concentration of agent applied and T is the time for which the agent is applied, so k is inversely proportional to dose (C·T is collectively called dose). Phenol coefficient test is best known screening test in which potency of a disinfectant is compared with that of phenol. A series of a dilutions of phenol and the disinfectant 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 exposure, but not at 5min. is used to calculate the phenol coefficient. This is done by dividing the resiprocal of the appropriate phenol dilution. Read more: http://wiki.answers.com/Q/Phenol_coefficien t_test_in_microbiology#ixzz1t6kiHZGL