^Average RFU were calculated by subtracting fluorescence of identical wells without NPN,
*NPN-uptake value is a ratio of relative fluorescence of the test well containing NPBD, Polymyxin B or EDTA, and the relative fluorescence of the control well containing HEPES buffer alone. EDTA and polymyxin B are positive controls which disrupt the OM allowing penetration of NPN into the lipid bilayer.