FIG. 2.

Comparison of expected and observed killing activities of cefepime plus amikacin (A), amikacin plus levofloxacin (B), and cefepime plus levofloxacin (C). The red mesh surface is the expected killing activity of the antimicrobial agent combination, and the black dots are the observed killing. When a black dot is below the red mesh surface, the observed killing is more than the expected killing (synergism). On the other hand, when a black dot is above the red mesh surface, the observed killing is less than the expected killing (antagonism). The overall killing over the concentration ranges examined was assessed by computing the VUP. Synergy and antagonism were defined as interactive index (VUP_observed/VUP_expected) values of <1 and >1, respectively.