Phenol coefficient

As a disiafectant or antiseptic, phenol [108-95-2] (carboHc acid) is mosdy of historical iaterest. However, its extensive use continues ia both iavestigative and analytical microbiology, eg, as ia the AO AC phenol coefficient and use-dilution methods. 

Although resorcinol [108-46-3], C H O, a dihydric phenol, is a comparatively weak bactericide, a nuclear-substituted alkyl derivative, -hexylresorcinol [136-77-6], has a phenol coefficient of 45, and has had considerable use as a topical antiseptic. 

Lysol consists of a mixture of the three cresol isomers solubilized using a soap prepared from linseed oil and potassium hydroxide, to form a clear solution on dilution. Most vegetative pathogens, including mycobacteria, are killed in 15 minutes by 0.3—0.6% lysol. Lysol has a phenol coefficient of 2. Bacterial spores are very resistant. Lysol is also the name of a proprietary product, the formula of which has changed over the years other phenols have been substituted for the cresols. 

Sudol uses fractions of coal tar rich in xylenols and ethylphenols. It is much more active and less corrosive than lysol, and remains more active in the presence of organic matter. The phenol coefficients of sudol against Mycobacterium tuberculosis, Staphylococcus aureus, and Pseudomonas aeruginosa are 6.3, 6, and 4, respectively. It also is slowly sporicidal (97). 

Phenol Coefficient Test. The first important attempt at standardizing testing methods was known as the phenol coefficient test (96). It has been modified several times, and is an official AO AC screening test recognized by EPA and PDA. The phenol coefficient test compares the activity of disinfectants to that of phenol, under specific conditions, to give a number that measures the activity of the chemical tested with respect to that of phenol, ie, the phenol coefficient. The AO AC method employs visual examination of bacterial growth in a nutrient medium. The Kelsey-Sykes test (1969) is a modified method popular in British circles. 

Some tests of the AO AC (309,310) are Hsted in Table 10. The phenol coefficient test employs three test organisms and a standard concentration of... 

Available Chlorine Test. The chlorine germicidal equivalent concentration test is a practical-type test. It is called a capacity test. Under practical conditions of use, a container of disinfectant might receive many soiled, contaminated instniments or other items to be disinfected. Eventually, the capacity of the disinfectant to serve its function would be overloaded due to reaction with the accumulated organic matter and organisms. The chlorine germicidal equivalent concentration test compares the load of a culture of bacteria that a concentration of a disinfectant will absorb and still kill bacteria, as compared to standard concentrations of sodium hypochlorite tested similarly. In the test, 10 successive additions of the test culture are added to each of 3 concentrations of the hypochlorite. One min after each addition a sample is transferred to the subculture medium and the next addition is made 1.5 min after the previous one. The disinfectant is then evaluated in a manner similar to the phenol coefficient test. For equivalence, the disinfectant must yield the same number of negative tubes as one of the chlorine standards. 

Phenol no longer plays any significant role as an antibacterial agent. It is of historical interest, since it was introduced by Lister in 1867 as an antiseptic and has been used as a standard for comparison with other disinfectants, which are then given a phenol coefficient in tests such as the Rideal-Walker test. 

They may be subdivided into phenol coefficient-type tests, of which there are many, quantitative suspension tests (which measure the rate at which test organisms are killed) and tests carried out at use-dilutions. 

PHENOL COEFFICIENT. In determining the effectiveness of a disinfectant using phenol as a standard of comparison, the phenol coefficient is a value obtained by dividing the highest dilution of the test disinfectant by the highest dilution of phenol that sterilizes a given culture of bacteria under standard conditions of time and temperature. 

Joseph Lister introduced phenol (carbolic acid) as a disinfectant in 1967. It has been the standard disinfectant to which other disinfectants are compared under the same conditions. The result of this comparison is the phenol coefficient. Salmonella typhi, a pathogen of the digestive system, and Staphlococcus aureus, a common wound pathogen, are typically used to determine phenol coefficients. A disinfectant with a phenol coefficient of 1.0 has the same effectiveness as phenol (Dorland s Illustrated Medical Dictionar). A coefficient less than 1.0 means that the disinfectant is less effective than phenol and greater than 1.0 is more effective than phenol. Phenol coefficients are reported separately for the different test organisms. 

The procedure for determining the phenol coefficient is pervasion throughout the published literature, including a summary description by Black (2005), and examples of phenol coefficients are listed in the following table (Table A.l). 

Table A.l Phenol coefficients of common agents (Black 2002)...

The phenol coefficient provides an acceptable means of evaluating the effectiveness of chemical agents derived from phenol, but it is less acceptable for other agents. Another problem is that the materials in which organisms may affect the usefulness of a chemical agent by complexing with it or inactivating it. These effects are not reflected in the phenol coefficient number. 

Where possible, activity has been expressed as log 1/C (i.e., pC) where C is the molar concentration required to cause a standard response (such as EDr)0, MIC, or LDioo). In many instances the intercepts of these equations can be compared. Where activity is expressed in other units, such comparisons are not possible. In a few examples the relative value, PC, the molar phenol coefficient, has been used. In Tables Ila-d new data not previously correlated are assembled. 

The mixture occurs as a yellow to brownish-yellow liquid that has a characteristic odor of creosote. Cresol is obtained from coal tar or petroleum by alkaline extraction into aqueous medium, acidifleation, and fractional distillation. The mixture is an inexpensive antiseptic and disinfectant. It possesses a phenol coefficient of 2.. >. Cresol is sparingly soluble in water, although alcohols and other organic solvents will. solubili/e it. The drawback to its use as an antiseptic is its unpleasant txlor. 

Sicnlanis. 2IK-22 . 2lKi cla sificaiinn of. 2IH. 21 Hi effeciiveness of. evaluation of. 219 improper use of. 219 phenol coefficient for. 221 Sterile capreomycin sulfate. 259. Sterile conicutnipin zinc hydroxide suspension. 842-H43. H42i... 

Phenol coefficient tests were developed in the early 20th century when typhoid fever was a significant public health problem and phenolics were used to disinfect contaminated utensils and other inanimate objects. Details of such tests can be found in earlier editions of this book. However, as non-phenolic disinfectants became more widely available, tests that more closely paralleled the conditions under which disinfectants were being used (e.g. blood spills) and which included a more diverse range of microbial types (e.g. viruses, bacteria, fungi, protozoa) were developed. Evaluation of a disinfectant s efficacy was based on its ability to kill microbes, i.e. its cidal activity, under environmental conditions mimicking as closely as possible real life situations. As an essential component of each test was a final viability assay, removal or neutralization of any residual disinfectant became a significant consideration. 

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