Permeability of Pseudomonas aeruginosa outer membrane to hydrophilic solutes

Abstract

P. aeruginosa is usually resistant to a wide variety of antibacterial agents, and it has been inferred, on the basis of indirect evidence, that this was due to the low permeability of its outer membrane. The permeability of P. aeruginosa outer membrane was determined directly by measuring the rates of hydrolysis of cephacetrile, cephaloridine and various phosphate esters by hydrolytic enzymes located in the periplasm. The permeabiity to these compounds was .apprx. 100-fold lower than in the outer membrane of Escherichia coli K-12. The apparent Km values for active transport of various C and energy source compounds were typically higher than 20 .mu.M in P. aeruginosa, in contrast to E. coli in which the values are usually lower than 5 .mu.M. These results are also consistent with the notion that the P. aeruginosa outer membrane indeed has a low permeabiity to most hydrophilic compounds and that this membrane acts as a rate-limiting step in active transport processes with high Vmax values.