Changes in S. Typhimurium invasiveness at early- and late-log growth after tetracycline exposure. Invasion assays were performed on S. Typhimurium isolates grown to either early- or late-log phase and exposed to four different tetracycline concentrations (0, 1, 4, and 16 μg/ml) for 30 minutes. Changes in invasion were normalized to the control dose (0 μg/ml) for each isolate at (A) early-log and (B) late-log growth phase. The “*” indicates a significant change based on the pre-normalized data. The numbers in parentheses indicate percent invasion at the control dose (0 μg/ml) for each isolate.