[Selection of resistant variants by broad spectrum beta-lactam antibiotics: to what extent is there cross resistance between imipenem and other beta-lactam antibiotics?].

Resistant variants can be selected in the presence of most of the recently developed beta-lactam antibiotics thus resulting in cross resistance between penicillin-, cephalosporin- and monocyclic derivatives except for imipenem. Among the Enterobacteriaceae-resistant so-called beta-lactamase-overproducing variants can be selected in some species in the presence of various broad-spectrum beta-lactams except for imipenem. However, imipenem-resistant variants can be selected from clinical Pseudomonas aeruginosa isolates in a frequency comparable to those obtained for other beta-lactams. Imipenem resistance in Pseudomonas aeruginosa is presently understood to be independent of either enzymatic degradation or an alteration of the penicillin-binding proteins; moreover, it has to be attributed to characteristic changes of the outer membrane proteins, thus explaining imipenem resistance due to impaired penetration. Consequently, resistance to imipenem in Pseudomonas aeruginosa has to be considered independent of resistance to other beta-lactams.