A Novel Insertion Sequence, IS Pa26 , in oprD of Pseudomonas aeruginosa Is Associated with Carbapenem Resistance

Carbapenems are frequently used to treat Pseudomonas aeruginosa; however, resistance to the carbapenems is emerging rapidly (9). Mutations or deletions in oprD (3, 2, 8) commonly result in lack of OprD expression, blocking the entry of imipenem into the cell and resulting in resistance to this drug (6). More recently, insertional inactivation of oprD by the insertion sequence (IS) elements ISPa1328 and ISPa1635 was described (7). Previously, we showed that imipenem resistance in P. aeruginosa was due to point mutations and deletions in oprD; IS elements were not detected in the isolates (3). To determine whether IS elements play a role in imipenem resistance in more recent isolates, we screened for their presence in oprD in isolates from two local hospitals.