Fig. 2

Synergistical bactericidal activity between SIM and polymyxins against S. aureus. Time-inhibition curves of SIM (1 µg/mL) and polymyxins (8 µg/mL) alone or in combination against USA300 (A) and ATCC 43,300 (B), respectively. Viable cells counting at the time point of 12 h at the highest gradient concentrations that can be well-counted for USA300 (C) and ATCC 43,300 (D), respectively. (E) Representative images of anti-planktonic bacterial effect of 1 µg/mL SIM alone or combined with 16 µg/mL PB(S) or 4 µg/mL PE against ATCC 43,300 by SYTO9 (green) and PI (red) staining. (F) Quantification of SYTO9/PI fluorescence intensity. (G) Sequential passaging resistance development of S. aureus USA300 treated with PB(S)/PE in the presence of sub-MIC (0.5 µg/mL) of SIM; (H) Drug combination between SIM and polymyxins against type strains and clinical isolates. *: P < 0.05; **: P < 0.01