RESUMEN
Sub-minimum inhibitory concentration [S-MIC] can induce changes in morphology, virulence factors and biochemical properties of bacterial pathogens. The goal of this study is to determine the Sub-MIC effect of ciprofloxacin and ampicillin on the haemolytic activity of E. coli. Two clinical isolates of E. coli with high haemolytic activity was selected. Changes in haemolytic activity of the isolates was assessed after exposing them to MIC and Sub-MIC of ciprofloxacin and ampicillin. Ciprofloxacin decreased haemolytic activity at 1/2, 1/4 and 1/8 Sub-MIC, whereas ampicillin showed no effect on haemolytic activity. We conclude that Sub-MIC concentrations of ciprofloxacin decreased the haemolytic activity of E. coli, whereas ampicillin had no such effect