MEROPENEM PERMEATION THROUGH THE OUTER-MEMBRANE OF PSEUDOMONAS-AERUGINOSA CAN INVOLVE PATHWAYS OTHER THAN THE OPRD PORIN CHANNEL

The outer membrane protein (OMP) OprD is the major channel through whi ch carbapenems permeate the outer membrane of Pseudomonas aeruginosa. In this study, we analyzed the OMP profiles of several P. aeruginosa c linical isolates showing diminished susceptibility to imipenem while r emaining susceptible to meropenem. All these isolates lacked OprD or s howed a reduced expression of this porin. Susceptibility to meropenem was thus independent of the level of OprD expression, indicating that the antimicrobial could be taken up via an alternative route. The leve l of expression of OprC (70 kD) was also unrelated to meropenem suscep tibility. Nevertheless, OMPs OprF and OprE were expressed by all isola tes, suggesting that in the absence of OprD, these porins might be inv olved in the permeation of meropenem.