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. 2020 Feb 12;6:6. doi: 10.1038/s41522-020-0116-3

Fig. 1. Effect of synergy between cecropin A (CecA) and nalidixic acid (NAL) on planktonic and biofilm-forming uropathogenic Escherichia coli cells.

Fig. 1

a Time-kill curves of CecA (50 μg/ml), NAL (0.5 ng/ml), and their combination against strain CFT073. Cells were treated with CecA 1 (50 μg/ml), CecA 2 (75 μg/ml), NAL (0.5 ng/ml), or CecA (50 μg/ml) + NAL (0.5 ng/ml) to determine b hemolysis of porcine erythrocytes in comparison to 10% Triton X-100 (control), and c the viability of BHK-21 fibroblast in comparison to untreated control. Kaplan-Meier plots of CFT073-infected G. mellonella survival after treatment with d CecA (50 μg/ml), e NAL (0.5 ng/ml), and f their combination +/− protease inhibitor (PI). g–j Scanning and k–n transmission electronic microscopy analysis of biofilm structures formed by CFT073 following treatment with CecA (50 μg/ml) ± NAL (0.5 ng/ml). g–n The biofilm-containing discs were supplemented with h, l NAL, i, m CecA, or j, n their combination in fresh LB medium and incubated for another 24 h. Biofilm-forming discs grown in LB medium without supplements were used as controls (g, k). Representative images are shown (scale bar = 2 μm). White arrow heads show intercellular filaments (g–j), black short arrow heads indicate cytoplasm density (k–n), and black arrows show cell debris (m, n). o Percentage inhibition of CFT073 biofilms by NAL (0.5 ng/ml) or CecA (50 μg/ml) compared to their combination after 48 h. p Percentage eradication of pre-formed CFT073 biofilms by NAL (0.5 ng/ml) or CecA (50 μg/ml) compared to their combination. q CFT073 adaptation to NAL (20 μg/ml) or the CecA (20 μg/ml) + NAL (0.5 ng/ml) combination was determined by analyzing bacterial growth after repeated exposure to antimicrobials for 5 days. The figure represents bacterial growth at day 5 with reference to day 1 after antimicrobial exposure. Values are means with standard errors: n = 4 (panels a and q), n = 3 (panels b–f and o–p). Significance was determined by one-way ANOVA, Dunnett’s multiple comparison test (b, c, o, p), Holm-Šídák correction (q) (*P < 0.05; **P < 0.005; ***P < 0.0005).