The phenol coefficient test has been employed for determining the germicidal efficiency of disinfectants for over 30 years since Rideal and Walker developed their original method in 1903 (1). In addition to being a satisfactory index of the germicidal value of phenol like disinfectants, the phenol coefficient is used as basis for determining the dilutions, which may safely be employed in practice. The phenol coefficient of each disinfectant was first determined by the Food and Drug Administration method, 1931 (2). Since then there is no standard method for testing disinfectants under practical conditions. Synthetic Broth is prepared, based on the formulation described by Wright and Mundy (3) and is recommended by AOAC (4) for determining phenol coefficients of disinfectants.
Variability in test cultures affects germicide testing. This medium minimizes variability of cultures and of media. It contains nutrients necessary for the growth of Salmonella Typhi , Staphylococcus aureus and Pseudomonas aeruginosa . These media are used for growing the inoculum and for subcultures used for the dilutions of disinfectant under test.
Directions: Suspend 16.9 grams in 1000 ml distilled water. Heat if necessary to dissolve the medium completely. Dispense 10 ml amounts in 20x150 mm culture tubes and sterilize by autoclaving at 15 lbs pressure (121°C) for 15 minutes. Cool to room temperature and just before use, aseptically add 0.1 ml of 10% sterile dextrose solution.