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. 2021 Oct 20;12:760017. doi: 10.3389/fmicb.2021.760017

FIGURE 1.

FIGURE 1

In contrast to another ribosome-targeting antibiotic spiramycin (SPR), erythromycin (ERY) does not suppress trimethoprim (TMP) when tested against a crl-deficient MG1655 strain. (A) Schematic of different drug-drug interaction isoboles in a two-dimensional drug concentration space. Loewe additivity of drug-drug interactions is used for quantifying effects of drug combinations. Lines of constant inhibition (isoboles) in the 2D drug concentration space represent combinations of drugs A and B that result in same normalized growth rate. The four types of interactions shown are synergistic (green), additive (red), antagonistic (orange) and suppressive (blue). (B) TMP and ERY show almost additive interaction against crl-deficient E. coli MG1655. Isoboles in grayscale represent exponential growth rates normalized to that of the no-antibiotic treatment control in 2D concentration space. When tested against a crl-deficient E. coli MG1655 strain, ERY and TMP show an additive interaction. In contrast, SPR exerted a mildly suppressive effect on TMP under the same experimental conditions.