Effect of siliconized latex urinary catheters on the activity of carbapenems against Pseudomonas aeruginosa strains with defined mutations in ampC, oprD, and genes coding for efflux systems.

The decreased activity of carbapenems against Pseudomonas aeruginosa in the presence of eluates from siliconized latex urinary catheters is related to the loss of OprD and the expression of a new outer membrane protein (OMP). To understand this phenomenon, the activity of carbapenems and quinolones against P. aeruginosa strains, some producing AmpC beta-lactamase (BL), OprD, MexA-MexB-OprM and MexE-MexF-OprN, were determined in Mueller-Hinton broth (MH) and in MH-containing eluates. OMP profiles and BL activities were also studied. Resistance to imipenem in P. aeruginosa grown in eluate is due to both the loss of OprD and expression of BL. For meropenem this phenomenon is related to both the loss of OprD and the integrity of MexA-MexB-OprM.