Cross-Resistance in Pseudomonas aeruginosa Resistant to Phenylethanol

The effects of benzalkonium, chlorhexidine, and phenyl-mercuric nitrate on exponential phase cultures of phenylethanol-sensitive Pseudomonas aeruginosa NCTC 6750 growing in nutrient broth and on phenylethanol-resistant cells growing in nutrient broth plus 0.2% phenylethanol v/v were determined. The resistant cultures grown in the presence of phenylethanol were more sensitive to benzalkonium, chlorhexidine, and phenylmercuric nitrate than phenylethanol-sensitive cells grown in nutrient broth. Phenyl-ethanol-antibacterial combinations were active against phenylethanol-resistant and phenylethanol-sensitive cultures. Survival times in solutions of benzalkonium, chlorhexidine, and phenylmercuric nitrate were determined for overnight P. aeruginosa cells grown in nutrient broth and for overnight P. aeruginosa cells trained to be resistant to phenylethanol and grown in nutrient broth plus 0.5% phenylethanol v/v. The cells grown in the presence of the phenylethanol were more sensitive to the action of the three antibacterials than the cells grown in nutrient broth alone.