Bactericidal activity and biochemical properties of LysAm24, LysECD7, and LysSi3. (a) Bactericidal activity of different concentrations of LysAm24 against A. baumannii Ts 50-16, LysECD7 against E. coli M15 and LysSi3 against the A. baumannii Ts 50-16 in exponential phase. Cell cultures without incubation with endolysins were used as controls. The number of surviving cells after 18 h is expressed as reduction in log10 CFU/mL compared to the control. NS, no statistical significance of the data compared to the untreated culture is observed (p > 0.05, Mann–Whitney test). (b) Activity of lysins against both exponentially growing cells (Exp) and stationary-phase cells (Stat) of A. baumannii Ts 50-16 without and in the presence of EDTA. The residual activity after 18 h of growth compared to the untreated culture is shown. NS, no statistical significance of the data compared to the exponential growth phase is observed (p > 0.05, Mann–Whitney test). (c) Effects of salts on the bactericidal activity against A. baumannii Ts 50-16. The residual activity after 18 h of growth compared to the untreated culture is shown. NS, no statistical significance of the data compared to the untreated culture is observed (p > 0.05, Mann–Whitney test). For all experiments, the mean values are shown (± standard error of the mean (SEM)) from three independent experiments. Asterisk (*) indicates significant effect on bactericidal activity.