Transcript Phenol coefficient - Fakultas Farmasi Unand

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 At 5-minute intervals, samples are withdrawn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.

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