Role of the outer membrane of Eschericia coli AG100 and Pseudomonas aeruginosa NCTC 6749 and resistance/susceptibility to monoterpenes of similar chemical structure

Four pairs of oxygenated terpenes, with closely related chemical structures but considerably different minimum inhibitory concentration values (1) aga inst F. aeruginosa or E. coh, showed differences in rate of cells killed ov er 2 h. Addition of polymyxin B nonapeptide (PMBN) as an outer membrane per meabilising agent was found to significantly increase the initial rates and overall numbers of cells killed for all compounds, The hydrocarbon limonen e and the ester geranyl acetate, normally inactive, were also investigated. Both compounds had little killing effect when added alone to the cells but did show an enhanced killing capacity upon the addition of PBMN.