The outer membrane of Pseudomonas aeruginosa NCTC 6749 contributes to its tolerance to the essential oil of Melaleuca alternifolia (tea tree oil)

Pseudomonas aeruginosa is less susceptible to the antimicrobial properties of tea tree oil than many bacteria and its tolerance is considered to be du e to its outer membrane. Polymyxin B nonapeptide (PMBN), which has no antib acterial action, was used to permeabilize the outer membrane. The addition of PMBN to Ps. aeruginosa NCTC 6749 markedly increased this organism's susc eptibility to tea tree oil and to its normally inert hydrocarbons, p-cymene and gamma-terpinene.