Evidence of permeation of
panipenem through the OprD (D2) channel of Pseudomonas aeruginosa outer membrane was shown by using OprD
protein-producing and -nonproducing strains which contained plasmid pHN4, which codes for L-1
beta-lactamase of Xanthomonas maltophilia. Permeation by
panipenem was determined by measuring hydrolysis of the
carbapenem by
beta-lactamase in the periplasmic space. Permeation by
panipenem was also determined by counting uptake of [14C]
panipenem into P. aeruginosa PAO1 and its OprD
protein-deficient mutant, and this permeation of PAO1 was inhibited by
L-lysine. These results indicate that
panipenem, as well as
imipenem, uses the OprD channel, which functions as a specific channel for diffusion of
basic amino acids.
Panipenem and
imipenem showed stronger activities against PAO1 and clinical isolates in human serum than in Mueller-Hinton broth, which contains more
amino acids than human serum does. The activities of the
carbapenems were reduced by addition of
L-lysine to human serum. Similar results were obtained with mouse serum and ascitic fluid. In contrast, such a change in the activities of
carbapenems was not observed with an OprD
protein-deficient mutant, suggesting that the main reason for the strong activities of
carbapenems in
biological fluids is a decrease in competition between the
antibiotics and
basic amino acids for permeation through the OprD channel.
Panipenem and
imipenem showed much stronger therapeutic efficacies against experimental
infections with P. aeruginosa in mice than did the reference
antibiotics. Their in vivo activities were more consistent with their MICs in
biological fluids than with those in Mueller-Hinton broth.