Figure 3

Time-kill curves, stability, toxicity, and pharmacological indexes of DLP2 and DLP4. (A) Time-kill curves of the two peptides and antibiotics against MRSA ATCC43300 in vitro. CK: without antibiotics and peptides. Results were given as mean ± SD (n = 3). (B) Inhibition of intracellular survival of MRSA ATCC43300 in RAW264.7 cells by peptides. PBS and vancomycin were used as negative and positive control, respectively. Results were given as mean ± SD (n = 3). Statistical significance of differences between experimental groups of animals was determined using the one-way ANOVA and Bonferroni multiple comparison. (*) indicates the significance between vancomycin or peptides and CK. **p < 0.01; ***p < 0.001; ****p < 0.0001. (C) The PAE (h) of different concentrations of peptides. (D,E) The FICI of each combination of different antibiotics with DLP2 (D) and DLP4 (E). Cip, ciprofloxacin; Kan, kanamycin; Cef, ceftriaxone; Van, vancomycin; Bac, bacitracin; Rif, rifampicin. (F) Effects of temperature on the peptide activity against S. aureus ATCC43300. (G) Hemolytic activity of the peptides against fresh mouse red blood cells (mRBCs). 0.1% Triton X-100 (triangle) served as positive control (100% hemolysis). (H) The cytotoxic activity of peptides and antibiotics against RAW264.7 monocytes. The 1 on the y-axis represents 100% survival. (I) Drug resistance development profiles of S. aureus exposed to sub-MIC concentrations of DLP2, DLP4, ceftriaxone and ciprofloxacin. A representative of four independent experiments is shown.