Antimicrobial susceptibility testing

The susceptibility of the C. jejuni strains to six quinolones was examined by broth microdilution method. The minimum inhibitory concentration (MIC) was determined to assess growth inhibition exhibited by each quinolone according to the criteria of the Clinical and Laboratory Standards Institute (CLSI) (27). Each strain was cultured on MH agar plate for 48 hours, and multiple colonies were then suspended in MH broth. The turbidity of the bacterial suspension was adjusted with 0.5 McFarland standards. An adjusted bacterial inoculum was added to each well of a sterile 96-well plate containing the test concentrations of quinolones. After the incubation for 48 hours at 37°C, the lowest concentration at which no bacterial growth was observed with the naked eye was designated as MIC. This examination was run in triplicate for each strain by quinolone to confirm reproducibility.