Figure 4.

Effects of combinations of AMPs with antibiotics showing antibacterial synergy on membrane permeability of E. coli ML-35p. (A) Permeability of the inner membrane for a chromogenic marker o-nitrophenyl-β-D-galactoside (ONPG). ¼ of minimal inhibitory concentrations (MICs) of antimicrobial peptides (AMPs) and antibiotics were used when alone, and ¼ MIC of AMP + ¼ MIC of antibiotic when in combination. Curves illustrate ONPG degradation by the cytoplasmic β-galactosidase of bacteria, when the membranes are damaged by test substances. Curves slope and the time of their rising to the plateau correspond to the extent of this damage. (B) Permeability of the outer membrane for a chromogenic marker nitrocefin under the effect of combination of lysozyme with polymyxin B. Outer membrane permeability was examined similarly to the inner membrane except for the chromogenic marker being used was nitrocefin in concentration of 20 μM and the OD measurement was performed at 486 nm. Nitrocefin is a substrate for the periplasmic β-lactamase of the bacteria. RIF, rifampicin; PMB, polymyxin B; GEN, gentamicin; OFL, ofloxacin; OX, oxacillin.