Adaptive alterations in the outer membrane of gram-negative bacteria during human infection.

The outer membrane of gram-negative bacteria is a dynamic structure that is capable of altering its ultrastructure and chemistry in order to adapt to changes in its environment. In human infections, outer-membrane alterations are known to play a role in mediating serum resistance, iron uptake, adaptation by Pseudomonas aeruginosa to colonization of the lungs of cystic fibrosis patients, and adaptive resistance to the polymyxin and aminoglycoside antibiotics. This adaptive antibiotic resistance is due to alterations in the cation binding sites within the outer membrane so that these cationic antibiotics can no longer penetrate through the membrane effectively. Adaptive resistance is not stable but is maintained only in the continued presence of the antibiotic. Hence, the role that this type of resistance to cationic antibiotics plays in clinical treatment of human infections remains inadequately assessed.