Figure 4

Isobologram analysis for biofilm cells of P. aeruginosa (a, b) PAO1, (c, d) 4219D and (e, f) 3470C. An additive-antagonistic effect is observed for the combination of tobramycin and bicarbonate against biofilm cells, in contrast to the strong synergistic effect observed with planktonic cells. Points along the isobologram represent the growth–no growth surface. (b, d, f) The orange shaded area represents the additive region, the purple shaded area represents the antagonistic region, and the green-shaded area represents the region of synergy.