*3.2. Scanning Electron Microscopy (SEM)*

To visualize the effect of ceragenins on the cell membrane, selected isolates were treated with a lead ceragenin, CSA-131, and their morphology was studied via SEM. Scanning electron photomicrographs of *Klebsiella pneumoniae*, *Moraxella* and *Legionella pneumophila* are shown in Figure 2. In the control without ceragenin treatment (Figure 2A,C,E), cells maintained normal morphology. In contrast, there were significant alterations in the morphology of cells treated with CSA-131 (Figure 2B,D,F). Treated cells are characterized by disruptions in the cell membrane along with increased roughness and wrinkling on the cell surface, confirming the membrane activity of ceragenins. Importantly, reported

morphological changes in this study are consistent with previous reports describing changes in the structure of bacteria and fungi after treatment with ceragenins [24,25].

**Figure 2.** Scanning electron photomicrograph of untreated (**A**) and treated (**B**) *Klebsiella pneumoniae*, untreated (**C**) and treated (**D**) *Moraxella* spp., untreated (**E**) and treated (**F**) *Legionella pneumophila* with 25 μg/mL CSA-131.
