Outer membrane proteins and lipopolysaccharide changes after exposure of Pseudomonas aeruginosa to antibacterial drugs.

Many studies show the low sensitivity of P. aeruginosa to antimicrobial agents, due to the permeability degree of the outer membrane (OM). Since the alterations of porins and lipopolysaccharides (LPS) are responsible for permeability to antibacterial drugs, the aim of this study was to evaluate the sub-M.I.C. effects of different antibiotics on the OM components. The M.I.C.s of five P. aeruginosa strains were determined and sub-M.I.C.s. versus PD-131,628, a new difluoroquinolone, aztreonam and netilmicin were calculated. The OM components were extracted before and after contact with the antibacterial drugs. We noted a decrease in M.I.C. values in two strains, and simultaneously an increase in the 19 and 38 Kd bands after using aztreonam. The M.I.C.s tended to increase in three strains after using netilmicin. The electrophoresis profile showed a decrease in the 38, 41 and 45 Kd bands and in one strain also in the 19 Kd band. The use of the quinolone did not significantly modify the M.I.C. values, although an evident increase in 38 and 41 Kd bands occurred in three strains. LPS alterations were observed with aztreonam and netilmicin, but not when PD 131,628 was used.