Fig 2.

Effects of various subinhibitory concentrations of ciprofloxacin (CIP), meropenem (MEM), azithromycin (AZN), rifaximin (RIF), tigecycline (TGC), and chloramphenicol (CHL) on Stx2 production in EHEC O104:H4 outbreak isolates LB226692 (A) and LB226806 (B) and EHEC O157:H7 strain EDL933 (C). Data show fold increases in Stx2 titers (indicating Stx2 production) compared to those of antibiotic-free controls (defined as 1) and are means ± standard deviations for four independent experiments. All antibiotics were tested at 1/2 to 1/16 MIC, and rifaximin was also tested at 1/32 and 1/64 MIC. *, P < 0.001; #, P ≤ 0.05 (unpaired Student's t test).