Antibacterial activity and agglutination.

The number of E. coli after in vitro incubation with recombinant proPO fragments or GFP as a control, compared with a buffer control (A), was determined. All experiments were repeated at least three times (N = 3). Each bar represents the mean ± SEM, and *** P<0.001 indicates significant differences between the treatment and Tris-HCl. The data were analyzed by one-way ANOVA. E. coli observed by light microscopy after treatment with the recombinant fragments. The scale bars represent 10 µm (B). Changes in bacterial morphology after treatment with the proPO-ppA fragment as observed by SEM (C–J). After 15 min of incubation with proPO-ppA (C) or GFP (D), cell wall disruption started to appear and is reflected by longitudinal lines (black arrows in C) in the proPO-ppA treatment. The scale bars represent 1 µm. After 40 min of incubation with Tris-HCl (E), proPO-ppA (F), and GFP (G), agglutination was clearly observed in the proPO-ppA samples. The scale bars represent 10 µm. The E. coli cells were clearly distorted after proPO-ppA treatment (H–I) in contrast to the GFP treatment (J). The pictures shown in (H) and (I) were taken from different areas. The scale bars represent 1 µm.