Antipseudomonal Effect of Polymyxin and Phenylethanol

The effect of subinhibitory concentrations of phenylethanol and polymyxin, alone and in combination, on the growth rate of phenylethanol-sensitive and -resistant or polymyxin-sensitive and -resistant Pseudomonas aeruginosa was determined. The combination had an additive effect on sensitive P. aeruginosa, while the behavior of the resistant strains indicated that cross-resistance occurs between polymyxin and phenylethanol, which was confirmed by sterilization time measurements. It is suggested that there is no cross-resistance between polymyxin and either benzalkonium chloride or chlorhexidine acetate.