Fig. 1

16-membered ring macrolide antibiotics induce ermB expression. A The structure of the ermB-based pGEX reporter plasmid. B Chemical structures of the macrolide antibiotics used in this work. C Agar diffusion assays of cells transformed with the reporter plasmid containing the ermBL-lacZα or ermCL-lacZα reporter grown on plates supplemented with IPTG and X-gal; each filter disc was spotted with erythromycin (Ery), spiramycin (Spi), tylosin (Tyl), chloramphenicol (Chl) and DMSO. D-E β-Galactosidase activity assays of the ermBL or ermCL-lacZα reporter gene on titration of erythromycin, spiramycin and tylosin. Miller units of β-galactosidase activity are shown on the Y-axis. The different concentrations of antibiotics are shown on the X-axis. The error bars correspond to the SEM of three independent experiments. The number on the top of each bar represents the largest fold change in beta-gal activity between the antibiotic and DMSO group. ***P < 0.001; (unpaired two-tailed Student’s t test)