[Characterization of imipenem resistance in Pseudomonas aeruginosa: decreased phenotypic expression of outer membrane proteins D1 and D2].

Imipenem-resistant variants can be selected from clinical Pseudomonas aeruginosa isolates in a frequency of 10(-8) to 10(-7) and 10(-5) in a single strain. In any case, there was no cross resistance between imipenem and other beta-lactams. In all IMI variants the induction potency of imipenem for the chromosomally-mediated Id beta-lactamase was markedly diminished as compared to the corresponding parent strains. Moreover, in all imipenem-resistant variants as well as in imipenem-resistant clinical isolates phenotypic expression of either a 46,000 dalton or a 47,000 dalton outer membrane protein was marginal; these proteins could be identified as proteins D1 and D2. These findings suggest a penetration barrier responsible for imipenem-resistance in Pseudomonas aeruginosa.