The Effect of pH and Temperature on Phenol Coefficients of Two Common Disinfectants Using Clinical Isolates of Escherichia coli and Staphylococcus aureus

Aims: The aim of this study is to evaluate the efficacy of two disinfectants, Jik and Roberts, under use-conditions against some hospital isolates using their phenol coefficient. The effects of pH and temperature on the phenol coefficients were also tested. Phenol coefficient still remains a valuable means of determining the effectiveness of disinfectants, even though phenol is no longer commonly used for disinfection.

Materials and Methods: Bacteria were isolated and identified using standard microbiological procedures from samples collected from the skin of patients and hospital environments like beddings, floors and trawlers. A 5% (w/v) solution of phenol and 5% (v/v) solution of disinfectants were used for determination of their phenol coefficients on standardized organisms containing about 1.5x108 cfu/ml. The effect of temperature was determined at 4ºC and 45ºC, while that of pH was determined at pH 1 and 13.

Results: The results showed that Staphylococcus aureus was more susceptible to both disinfectants. Jik had a higher phenol coefficient for the test organisms (16 and 8) compared to Roberts (4 and 2) for S. aureus and Escherichia coli respectively. Both temperature and pH had a direct effect on the antibacterial activities of the disinfectants. The phenol coefficient was higher for both organisms at 45ºC than at 4ºC for Roberts. In the case of Jik, the phenol coefficient reduced as the temperature was increased to 45ºC. At pH 13, Jik gave a higher phenol coefficient, while Roberts gave a higher phenol coefficient at pH 1.

Conclusions: Temperature enhances the performance of Roberts but has a negative effect on that of Jik. Roberts performs better at acidic pH while Jik performs better at alkaline pH. For disinfection purposes, it is recommended that different types of disinfectants be employed in the rotation to help prevent the development of resistant strains of microorganisms.