[The concentrations of fluoroquinolones in prevention of Staphylococcus epidermidis from mutant in ocular surface]

To examine the mutant prevention concentration (MPC) of the four fluoroquinolones to Staphylococcus epidermidis from ocular in vitro, and to compare the MPCs to the minimal inhibitory concentrations (MICs).

The MICs of the ciprofloxacin, ofloxacin, levofloxacin and gatifloxacin were determined by the standard twofold agar dilution methods of the National Committee for Clinical Laboratory Standards (NCCLS). The single colony of Staphylococcus epidermidis on the blood agar plate was inoculated into Muller Hinton broth. The turbidity of the actively growing broth culture was adjusted to 1 x 10(8) cfu/ml and then the broth was diluted 1:10 and 1 microl of the diluted broth was inoculated on the Muller Hinton agar surface for each drug in different concentrations. The final inoculum was approximately 10(4) cfu. The MPCs were measured by mix-bacterial methods. The concentrations of the drugs used in MPC's determination were determined according to the drug's MIC(50) to the bacteria. 1 ml of drug's broth and 19 ml suspension of the bacteria and Muller Hinton agar were added into one plate with the final 10(10) cfu of inoculum.

The lowest MIC(90) was gatifloxacin at 0.25 mg/L, the medium MIC(90) is levofloxacin at 0.50 mg/L, the highest MIC(90) at 1.00 mg/L was detected in ciprofloxacin and ofloxacin. The MPC(50) and MPC(90) for gatifloxacin were 1.00 mg/L and 2.00 mg/L respectively, which were the lowest concentration among the four drugs tested. The same parameter of the MPC(50) (2.00 mg/L) and MPC(90) (4.00 mg/L) was obtained in levofloxacin and ciprofloxacin, the MPC(50) for ofloxacin was as high as levofloxacin and ciprofloxacin at 2.00 mg/L but its MPC(90) was 8.00 mg/L.

The new fluoroquinolones shows high effect on anti-bacterial Staphylococcus epidermidis. Gatifloxacin and levofloxacin may play a role in prevention Staphylococcus epidermidis from mutation.