Comparison of agar dilution, microtitre broth dilution and tube macrodilution susceptibility testing of ciprofloxacin against several pathogens at two different inocula.

The susceptibility of six different genera of organisms to ciprofloxacin was determined by the tube macrodilution, broth microdilution and the agar dilution methods. The minimal inhibitory concentrations of ciprofloxacin determined by the broth microdilution and the agar dilution methods correlated well with each other, but in general the tube macrodilution technique gave somewhat higher results. Raising the initial inoculum of the tested organisms from 1 X 10(5) to 1 X 10(7) cfu/ml did not result in a significant increase in the minimal inhibitory or bactericidal concentrations of ciprofloxacin.