IN VITRO ANTIBACTERIAL EFFECT OF ENROFLOXACIN DETERMINED BY TIME-KILLING CURVES ANALYSIS

Minimal inhibitory concentrations (MIC) are used as in vitro reference values to describe the activity of antibacterial drugs against a given microbial strain. The effect of antibiotics over time could be assessed by time-dependent bactericidal (time-killing) curves. In this study, MIC, mutant prevention concentrations (MPC) and time-killing curves of enrofloxacin were investigated on a pathogenic E. coli O78/H12 strain, isolated from broiler chickens. The tested strain was sensitive with MIC=0.015 μg/mL. MPC value was considerably higher (4 μg/mL). Time-killing curves showed that enrofloxacin activity was better at concentrations higher than 1 μg/mL (16×MIC in serum) whereas at lower concentrations (0.06 μg/mL) bacterial counts increased after a 24-hour incubation. These curves, together with MPC could be used to design a therapeutical schedule for problematic E. coli infections in farms, as they depict the behaviour of pathogenic strains over time and provide information about the possibility for selection or presence of resistant microbial populations.