Role of porins in the antibiotic susceptibility of Pseudomonas aeruginosa: construction of mutants with deletions in the multiple porin genes.

We inserted deletions in the chromosomal genes of Pseudomonas aeruginosa coded for the outer membrane porins, proteins C, D2, or E1, and all possible combinations of these proteins by the gene replacement technique and selecting for imipenem-resistance. Determination of the minimum inhibitory concentrations of beta-lactams, fluoroquinolones, chloramphenicol and gentamicin in these mutants revealed that most mutants showed equal susceptibility to the porin-sufficient strain. The only exception was that imipenem and meropenem showed increased minimum inhibitory concentrations in all of the mutants lacking protein D2. These results firmly established that the P. aeruginosa porins identified so far form the pores do not accommodate the passage of most antipseudomonal antibiotics, with the exception of carbapenems.