| Objectives:The aim of this study was to investigate whether the mutant prevention concentration (MPC) and the ratio of MPC/minimal inhibitory concentration (MIC) ratio might be the efficacious parameters for rational applications of available antibacterial drugs in clinical treatment of H.pylori eradication by levofloxacin alone and combination with amoxicillin against H.pylori.Methods:1. Stock culture of H.pylori was inoculated on drug free Columbia agar base media with H.pylori nutrient supplements and 10% fetal calf serum under microaerophilic conditions, the drug sensitivity of 128 isolated H.pylori strains to levofloxacin and amoxicillin in our hospital in 2009 was detected by Kirby-Bauer test.2. H.pyloril strains were enriched in broth and adjusted to 1010 and 105 CFU/ml, the MIC and provisional mutant prevention concentration (MPCpr) of levofloxacin and amoxicillin against H.pylori were determined by agar two fold dilution method. H.pylori standard strain ATCC43504 was taken as control strain in this test, and then the MIC99 and MPC were calculated. The MIC for 90% of input cells (MIC90), the MPCpr for 90% of input cells (MPCpr) and MPCpr/MIC ratio were calculated for the clinical isolates.3. The MPCpr and MPCpr/MIC against 12 H.pylori of clinical isolates by Levofloxacin alone were compared respectively with those by Levofloxacin (2n×MIC) combined with amoxicillin (0.5 mg/l). The changes of MPCpr/MIC by levofloxacin alone and combined with amoxicillin at concentration of 2n×MIC against H.pylori standard strain ATCC43504 were observed.Results: 1. The resistance rate of clinical H.pylori strains to levofloxacin was 9.38% in 2009, and significantly increased (P<0.05) compared to the data in 2007 (0) and 2008 (7.2%) in our hospital, whereas that to amoxicillin was only 2.34% in 2009 without differences (P>0.05) compared with the datum in 2007 (1.1%).2. The MIC90 of levofloxacin and amoxicillin for 12 H.pylori of clinical isolates were 0.50, 0.25 (mg/l), MPCpr90 were 8.00, 4.00 (mg/l), and selection index (MPCpr90/MIC90) were 16, 16 respectively. The MIC99 of levofloxacin and amoxicillin for H.pylori strain ATCC43504 were 0.048, 0.024 mg/l, MPC were 1.60, 1.60 (mg/l), respectively.3. When the amoxicillin (0.5 mg/l) was used in combination with levofloxacin, the MPCpr/MIC ratio against the clinical isolates decreased two to eight fold; The MPCpr/MIC ratio against the H.pylori strain ATCC43504 by levofloxacin combined with different concentrations of amoxicillin (2n×MIC) decreased gradually along with the increasing concentrations of amoxicillin. When the amoxicillin concentration was 0.5 mg/l, and MPCpr/MIC ratio became 4.00.Conclusion:1. The resistance rate of clinical H.pylori strains to levofloxacin had increased significantly in Suzhou from 2007 to 2009, while that to amoxicillin was still low.2. According to Pharmacokinetic parameters of levofloxacin and amoxicillin, when levofloxacin (500mg, once a day) or amoxicillin (1000mg, twice a day) was orally administered, the plasma concentrations of levofloxacin fell into the mutant selection window (The drug concentration range between the measured MIC and MPC values defines the MSW) for the entire dosage interval, the plasma concentrations of amoxicillin was above MPCpr90 for most the time, these datum suggested that the resistant mutant could be enriched easily in H.pylori for levofloxacin alone, but the amoxicillin was effective at restricting the selection of resistance. These data perhaps partly explain the differences of the resistance rates between levofloxacin and amoxicillin against H.pylori in practice. 3. The MPC/MIC ratios against H.pylori of clinical strains by levofloxacin combined with amoxicillin were significantly lower than by levofloxacin alone, so the antimicrobial combination can narrow the mutant selection window. This study demonstrated that the combination therapy may be effective at preventing the emergence of resistance in H. pylori.
|
PDF Full Text Request