Instability of in vitro resistance to imipenem in Pseudomonas aeruginosa

In 3 from 19 clinical isolates of Pseudomonas aeruginosa imipenem-resistant subpopulations could be detected in vitro. In comparison to their wild strains these imipenem-resistant cells were lacking an outer-membrane-protein of 50 kD. In the subpopulation derived from Pseudomonas aeruginosa 76 resistance to imipenem was found to be instable. It could be lost within a short period of time after subcultivation in the absence of imipenem. Cells with restored sensitivity to imipenem possess the outer membrane protein of 50 kD as the wild strain does.