To study the membrane-damaging action of lead cyclic peptides (15c and 16c) on live microbial cells, we used SEM to examine untreated and treated bacterial and fungal cells. The untreated microbial cells displayed smooth, intact surfaces and regular morphology (Figures 4B1, B4, B7, and B10). In contrast, treated microbial cells, especially bacteria, were visualized to have significant structural damage.