Prof. Dr. Marlina, MS., Apt.

Phenol coefficient  is a measure of the bactericidal activity of a chemical compound in relation to phenol.bactericidal 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.disinfecting standardized test

 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  At 5-minute intervals, samples are withdrawn from each dilution and used to inoculate a growth medium, which is incubated for two or more days and then examined the growth.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 coefficientRideal-WalkerRideal- Walker coefficient  and the U.S. Department of Agriculture method gives a U.S. Department of Agriculture coefficient.U.S. Department of Agriculture

 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.organic matter

 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: t_test_in_microbiology#ixzz1t6kiHZGL t_test_in_microbiology#ixzz1t6kiHZGL