Mean diarrhea score (±standard deviation [SD]) of weaned pigs challenged with ETEC: F4. Challenge was performed at d-2 and treatment with colistin sulfate (CS) at the dose of 50 000 IU/kg (trial 2) was started at d0 (36 h post challenge) and administered twice daily for a period of 5 days. Treatment with oral CS resulted in a statistically significant reduction in the diarrhea score of the challenged treated group compared to the challenged untreated group (p < 0.0001) between d2 and d4. Mean diarrhea score = sum of daily diarrhea score/number of animals. *: p < 0.0001.