Aromatic alcohols and their effect on Gram-negative bacteria, cocci and mycobacteria

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1Welsh School of Pharmacy and 2School of Molecular and Medical Biosciences, Cardiff University, Cardiff CF10 3XF, UK

Sir,

Phenethyl alcohol (2-phenylethanol; PEA, mol. wt 122.17) inhibits a range of Gram-negative bacteria, but not Pseudomonas fluorescens, at a concentration of 0.2% (2000 mg/L), whereas Gram-positive cocci, such as Staphylococcus aureus are inhibited at 0.5% w/v (5000 mg/L), with Enterococcus faecalis requiring still higher concentrations.1 PEA-containing media had earlier been suggested as a means of selecting for Gram-positive bacteria in mixed flora.2 Interestingly, Mycobacterium smegmatis and Mycobacterium phlei were also inhibited at 0.2%, suggesting that the solubility of PEA in lipids could play a major role in its selective action.1 However, Wilson et al.3 reported that PEA was only slightly less inhibitory to Staphylococcus aureus than Escherichia coli, and that the MIC for Pseudomonas aeruginosa was 0.46% (4600 mg/L).

As part of comprehensive studies of the responses to biocides of mycobacteria, other Gram-positive bacteria and Gram-negative organisms, it was decided to investigate the effects of PEA and of another, significantly more hydrophobic, aromatic alcohol (5-phenyl-1-pentanol; 5-PP, mol. wt 164.25) on some strains of Mycobacterium chelonae, M. smegmatis and Burkholderia cepacia. B. cepacia K56-2 triclosan- and chlorhexidine-susceptible mutants were isolated using a Tn5-pOT182 random mutagenesis system. Strain K56-2 is a genetically amenable clone of the genome sequencing strain J2315. A single strain used in disinfectant testing [EN 1276 (1997)] of each of E. coli, P. aeruginosa and S. aureus was included for comparative purposes. M. chelonae NCTC 946 is a glutaraldehyde-susceptible control, whereas M. chelonae strains Epping and Harefield are glutaraldehyde resistant but ortho-phthalaldehyde susceptible.4M. smegmatis LIMP7 is a derived mutant of M. smegmatis mc²155 with an altered cell envelope permeability. This mutant has a defective impA1 (inositol mono-phosphate phosphatase) gene, leading to a dramatic decrease in lipoarabinomannan synthesis.