Abstract

2-Phenoxyethanol (2-PE) is a biocide used as a preservative in pharmaceutical, cosmetic and perfumery formulations. It is known for its rapid bactericidal effect against a wide range of bacteria. In the present study, clinical samples of multi drug resistant (MDR)Pseudomonas aeruginosa and Escherichia coli were grown in an increasing sub-minimal inhibitory concentration of 2-PE to observe if adaptation could be obtained and consequently retrieval of antibiotic susceptibility to clinically used antibiotics. Minimal inhibitory concentration (MIC) of 2-PE was determined for both MDR E. coli   and  P. aeruginosa. Adaptation to the biocide was attempted by repeated sub- culturing of the isolates in increasing sub-minimal-inhibitory concentration of the biocide. E. coli was able to grow in the presence of sub-MIC of 2-PE for two passages only and a slight rise in MIC was observed. MDR P. aeruginosa rapidly obtained an adaptive resistance towards the biocide with an increase in MIC from 5.4 to 13.7g%. Antibiotic sensitivities for both, MDR and MDR-2-PE adapted E. coli and P. aeruginosa were detected. MDR2-PE resistant P. aeruginosa showed significant improvement in antibiotic sensitivity while no change was

observed with E. coli. Our results suggest an intriguing species specific link between biocide resistance and changes in antibiotic susceptibilities, findings that could be utilized in controlling the spread of antibiotic resistance and ambitiously improving the activity of some existing antibiotics.

Key words: Pseudomonas aeruginosa, 2-phenoxyethanol, antibiotic resistance.

Abbreviation

BC, Benzalkonium chloride; MIC, minimum inhibitory concentration; 2-PE, 2-phenoxyethanol; MDR, multi drug resistant; DMF, dimethylformamide; NB, nutrient broth; MHB, Mueller Hinton Broth.