Influence of environmental factors on inhibition of Aeromonas hydrophila activity in vitro by four quinolones

The effects of various pH values, Mg~(2+), calf blood serum and inoculum size of bacteria in the culture medium on the minimal inhibitory concentration (MIC) and minimal bactericidal concentration (MBC) of ciprofloxacin, difloxacin, enrofloxacin and danofloxacin against Aeromonas hydrophil were determined in vitro. The results showed that the MIC and MBC were the least for the four quinolone at pH 7 or 8, whereas the MIC and MBC significantly increased when the pH was either high or low. The MIC and MBC of ciprofloxacin and enrofloxacin increased with increae in the Mg~(2+)concentration, while the MIC of difloxacin remained stable when the Mg~(2+) between 0-2.0 μg/mL, and its MBC increased from 0.8-3.2 μg/mL, danofloxacin has the highest vitro activity at the 0.5 μg/mL of Mg~(2+), but activity began to reduce as the increasing of Mg~(2+). The MIC and MBC of four quinolones remain constant when the inoculum size of bacteria from 10~(2)-10~(5)(CFU/mL), the MIC and MBC began to increase only when it was 10~(6) CFU/mL. The blood serum has the significant influence on the vitro activity of quinolones, the activity reduced significantly of the quinolones.