Phenol Coefficient

A simple and brief presentation on the phenol coefficient with a video explanation of the test procedure.

1. PHENOL COEFFICIENT Prepared By Rahit Singha BMLT, MSc. Microbiology

2. INDEX INTRODUCTION DEFINITION OF PHENOL COEFFICIENT WHAT IS PHENOL COEFFICIENT CALCULATION OF PHENOL COEFFICIENT PHENOL COEFFICIENT TEST RIDEAL WALKER METHOD CHICK MARTIN TEST FACTORS AFFECTING PHENOL COEFFICIENT TEST CONCLUSION REFERENCES

3. INTRODUCTION Chemical disinfectants are categorized based on the power of their disinfection for  microbes  and  viruses . Strong disinfectants can kill  fungi ,  vegetative cells , endospores, and  pathogens . Extended use of disinfectants can result in sterilization.  Intermediate-level disinfectants  are less effective against certain viruses and endospores.  Low-level disinfectants  are ineffective against endospores and can kill some enveloped viruses and vegetative cells. The measure of the power of disinfection is required to appropriately suggest the application of a particular disinfectant. The effectiveness of chemical disinfectants can be measured using different methods, such as  qualitative suspension test ,  quantitative suspension test ,  Dilution test ,  Kelsey Sykes test ,  surface time kill test , etc. The  phenol coefficient   is one of the methods to determine the effectiveness of a disinfectant.

4. DEFINITION OF PHENOL COEFFICIENT The measure of the disinfecting power of a substance, determined by dividing the figure indicating the degree of dilution of the  disinfectant  that kills a  microorganism  within a given time by that indicating the degree of dilution of  phenol  killing the microorganism under similar conditions. The number obtained by dividing the degree of dilution of test disinfectant by the degree of dilution of phenol in a certain span of time.

5. If the number is greater than 1, it means that for given dilution, the test disinfectant is more powerful and can kill germs better than phenol. If the number obtained is less than 1, it means that for the given dilution, phenol is better at controlling germs

6. WHAT IS PHENOL COEFFICIENT Phenol is an aromatic compound and a carboxylic acid whose formula is C 6 H 6 O. Its structure is shown in the figure below: Figure : Structure of phenol

7. WHAT IS PHENOL COEFFICIENT Phenol   is recognized as one of the oldest antiseptic agents with excellent antifungal and antibacterial properties. At concentrations of 0.1 % to 1 %, it is bacteriostatic. At higher concentrations (from 1% to 2%), phenol is  fungicidal  and  bactericidal . Phenol can kill  Anthrax  spores (which cause severe skin lesions, lung infections, and intestine diseases) at 5% concentration within 48 hours. Although phenol has excellent antiseptic properties, it is not used as a common antiseptic due to its systemic toxicity on the  skin . Death can result from oral ingestion in significant quantities. Thus phenol is used for comparison of the power of disinfection of other disinfectants such as chlorine, ozone,  hydrogen peroxide , etc.

8. CALCULATION OF PHENOL COEFFICIENT Phenol coefficient is a number obtained by dividing dilution ratio test disinfectant with the dilution ratio of phenol under predetermined conditions. For instance, suppose phenol diluted to 1 part in 100 parts of diluent (1/100) is able to kill an organism in 10 minutes. Another disinfectant is diluted 1 part in 500 parts diluent (1/500) is able to kill organisms at the same time. So the phenol coefficient can be calculated as follows: Thus, the phenol coefficient is 5. It means that the test disinfectant is stronger than phenol in terms of disinfection. Figure  : Calculation of phenol coefficient

9. PHENOL COEFFICIENT TEST Two types of phenol coefficient tests are done: Rideal Walker method for phenol coefficient determination Chick Martin test

10. RIDEAL WALKER METHOD In 1903, Rideal Walker proposed a method to determine the power of a disinfectant in comparison with phenol.

11. RIDEAL WALKER METHOD The phenol coefficient can be calculated as: The limitation of the Rideal Walker method is that it does not account for the presence of any  organic matter . Moreover, the time for disinfection testing is too short.  This test is used only to determine the power of phenolic type disinfectants only.

12. CHICK MARTIN TEST Chick martin test incorporates the presence of organic matter as the test is not carried out in the water but yeast suspension or 4% dried human feces. The total time of the test is 30 minutes. Both  S. typhi  and  S. aureus  cultures are used to test the efficacy of disinfectants. The calculation method is the same as that Rideal Walker test.

13. FACTORS AFFECTING PHENOL COEFFICIENT TEST Four major factors affect the disinfectants and thus produce wrong results for phenol coefficient tests. These factors are temperature, pH, surface activity, and the presence of interfering substances. An increase in temperature has shown increased disinfectant properties. Optimal growth is achieved at pH between 6 to 8; thus, the recommended pH for the tests is 7.5. The surface-active compounds in low concentrations may increase the disinfectant power. Interfering substances such as certain salts may hinder disinfectant activity

14. CONCLUSION The phenol coefficient tests are designed specifically for determining the disinfection power of phenol-like disinfectants. However, it has been observed that the phenol coefficient is used for other purposes for which it is not applicable. Some chemicals whose structure and properties are completely different from phenol but are germicides (such as chlorine, picric acid, hydrogen peroxide, formalin, iodine, etc.) have been compared with phenol. In some cases, water-insoluble compounds are compared with phenol either in their pure form or diluted in other kinds of solvents. Such misuse of phenol coefficient creates confusion. It is also not recommended to use phenol coefficient for testing antiseptics because antiseptics are not used to kill  Bacillus typhosus  usually used in phenol tests. Different antiseptics kill different bacteria with varying antiseptic power. One example is tincture iodine, which is 760 times more disinfecting compared to 5 % phenol solution. However, in reality, tincture iodine is not 760 times more germicidal than 5 % phenol in practical conditions.

15. References Chem.Purdue. (2019). Phenol. Retrieved June 21, 2021, from https://www.chem.purdue.edu/jmol/molecules/phenol.html Lakomia, L. & Fong, E. (1999). Microbiology for health careers. Albany, NY: Delmar Publishers. Ononugbo, C., Reward, E., & Ike, A. (2018). The Effect of pH and Temperature on Phenol Coefficients of Two Common Disinfectants Using Clinical Isolates of Escherichia coli and Staphylococcus aureus .  Journal of Advances in Microbiology , 10(2), 1–7. https://doi.org/10.9734/jamb/2018/41376 Reddish, G. F. (1937). Limitations of the Phenol Coefficient. Industrial and Engineering Chemistry, 29(9), 1044–1047. https://doi.org/10.1021/ie50333a017

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