| Objective: The antibacterial effect, minimal inhibitory concentration and post antibiotic effect of Clarithromycin, Cefuroxime sodium separately and jointly against Staphylococcus Aureus and Streptococcus pneumonia were studied.Methods: 1. The minimal inhibitory concentration ?MIC? of Clarithromycin and Cefuroxime sodium against Staphylococcus Aureus and Streptococcus pneumonia were determined by agar plate dilution method when they are separately used and by chess board method when they are used in combination. The fractional inhibitory concentration ?FIC? was then calculated.Each agar plates containing various concentrations of clarithromycin,cefuroxime sodium, and clarithromycin plus cefuroxime sodium was inoculated with 1?1 bacterial suspension, the turbidity of which was 1.0×107 CFU·mL-1.These agar plates were incubated in incubatorat 35 ? for 18 to 24 h. If no bacteria growth was observed with naked eyes under lowest drug concentration,this concentration would be regarded as MIC.2. The mutant prevention concentration ?MPC? of Clarithromycin and Cefuroxime sodium against Staphylococcus Aureus and Streptococcus pneumonia were determined by agar plate dilution method and simple chess board method, respectively. The corresponding selection index SI ?MPC/MIC?was then calculated. 1010 CFU·mL-1 of Staphylococcus Aureus and Streptococcus pneumonia were enriched by meat infusion culture-medium. 0.1 ml of bacteria suspension with chosen turbidity was added to agar plates containing various concentrations of clarithromycin, cefuroxime sodium and clarithromycin plus cefuroxime sodium. The agar plates were uniformly coated with glass spreader and then incubated inincubator at 37 ? for 72 h. The lowest drug concentration under which no bacteria grew was determined as MPC.3. The infection model of neutropenic mouse thigh under Staphylococcus Aureus and Streptococcus pneumoniae were established. The post antibiotic effect ?PAE? of Clarithromycin and Cefuroxime sodium which were used separately and jointly on Staphylococcus Aureus and Streptococcus pneumoniae in vivo were measured by approach of plate colony counting. 150;mg·kg-1 and 100 mg·kg-1 cyclophosphamide were injected to mice abdomen on the first day and third day of experiment, respectively. 0.1 ml bacteria with antibiotics removed was injected into the femoral muscle of mice. This time was defined as 0 h after construction. Every six mice were killed at 0, 1, 2, 3, 4, 6, 8,10, 12 h after construction, respectively. These killed mice thigh muscle were immediately made into homogenate by adding pre-cooling sterilized physiological saline. The ratio of saline to muscle was 9:1. 10 ?l homogenate from each killed mice was inoculated on M-H agar plates and then incubated in incubator at 37 ? for 24 h. The colony counts were accordingly calculated. The PAE was defined as the time difference required for the colony counts in terms of CFU·mL-1 from antibiotic-treated tube was 10 times higher than that from without antibiotic-treated tube at 0 h under construction.Results: 1. The MIC of Clarithromycin and Cefuroxime sodium separately against Staphylococcus Aureus were both 4.0 ?g·mL-1 and fractional inhibitory concentration ?FIC=2.0? was observed under combination of Clarithromycin and Cefuroxime sodium. The MIC of Clarithromycin and Cefuroxime sodium separately against Streptococcus pneumonia were 0.0625?g·mL-1 and 16.0 ?g·mL-1, respectively. Similarly, fractional inhibitory concentration ?FIC=2.0? was observed for combination of Clarithromycin and Cefuroxime sodium.2. The MPC of Clarithromycin and Cefuroxime sodium separately against Staphylococcus Aureus were 25.6 ?g·mL-1 and 51.2 ?g·mL-1,respectively. SI of them was 6.4 and 12.8, respectively. The MPC of Clarithromycin decreased from 25.6 ?g·mL-1 when it was used alone to 8.0?g·mL-1 when it was combined with Cefuroxime sodium. Besides, SI reduced from 6.4 when it was used alone to 2.0 after combination with Cefuroxime sodium. The MPC of Cefuroxime sodium decreased from 51.2?g·mL-1 when used alone to 8.0 ?g·mL-1 when combined with Clarithromycin. SI decreased from 12.8 to 1.0. When Clarithromycin and Cefuroxime sodium were combined and each of them reached the value of 8.0 ?g·mL-1, it could inhibit the generation of resistant mutants.The MPC of Clarithromycin and Cefuroxime sodium separately against Streptococcus pneumonia were 1024.0 ?g·mL-1 and 256.0 ?g·mL-1 ,respectively. SI of them was 16384.0 and 16.0, respectively. The MPC of Clarithromycin decreased from 1024.0 ?g·mL-1 when it was used alone to 0.03125 ?g·mL-1 when it was combined with Cefuroxime sodium. Besides, SI of Clarithromycin reduced from 16384.0 when it was used alone to 0.5 after combination with Cefuroxime sodium. The MPC of Cefuroxime sodium decreased from 256.0 ?g·mL-1 when used alone to 8.0 ?g·mL-1 when combined with Clarithromycin. The SI of it decreased from 16.0 when used alone to 0.5 when combined with Clarithromycin.3. Both Clarithromycin and Cefuroxime sodium used separately and jointly brought about certain PAE against Staphylococcus Aureus in vivo. After statistical analysis, the differences between the groups seemed not significant.Besides, their combinations had indifferent effect on PAE against Staphylococcus Aureus.The Clarithromycin and Cefuroxime sodium used separately and jointly also brought about certain PAE against Streptococcus pneumonia in vivo.After comparison of PAE under same concentration but different drugs,statistically significant differences in PAEs were demonstrated between Clarithromycin and Clarithromycin plus Cefuroxime sodium?P<0.05? when the concentration was 2 MIC and 4 MIC. When the concentration was 8 MIC,statistically significant differences in PAEs were found between Clarithromycin and Cefuroxime sodium, between Clarithromycin and Clarithromycin plus Cefuroxime sodium?P<0.05?. With same drug but different concentrations, no significant differences in PAEs were found in Clarithromycin. For Clarithromycin and Clarithromycin plus Cefuroxime sodium, statistically significant differences in PAEs were found when the concentrations were between 2 MIC and 8 MIC ?P<0.05?. At low concentration ?2 MIC and 4 MIC?,Clarithromycin plus Cefuroxime sodium had addition effect on PAE against Streptococcus pneumonia. Under concentration of 8 MIC, Clarithromycin plus Cefuroxime sodium showed indifferent effect.Conclusion: 1. Indifferent effect is observed for combination of Clarithromycin and Cefuroxime sodium against Staphylococcus Aureus and Streptococcus pneumonia.2. The combination of Clarithromycin and Cefuroxime can reduce the MPC and SI of Staphylococcus Aureus, Streptococcus pneumonia but enhance the ability of anti-drug resistant mutants.3. The Clarithromycin and Cefuroxime sodium uses separately and jointly brought about certain PAE against Staphylococcus Aureus and Streptococcus pneumoniae in vivo. Besides, their combinations have indifferent effect on PAE against Staphylococcus Aureus under any concentration and showed either addition effect or indifferent effect on PAE against Streptococcus pneumoniae. The effect varied based on the concentration. |
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