The cell envelope of Gram-negative bacteria is a formidable biological barrier, inhibiting the
action of antibiotics by impeding their permeation into the intracellular environment. In-depth
understanding of permeation through this barrier remains a challenge, despite its critical role
in antibiotic activity. We therefore designed a divisible in vitro permeation model of the Gram-
negative bacterial cell envelope, mimicking its three essential structural elements, the inner
membrane and the periplasmic space as well as the outer membrane, on a Transwell setup …