In vitro effect of erythromycin and levofloxacin alone or in combination against ureaplasma urealyticum

OBJECTIVE To evaluate the effect of erythromycin and levofloxacin alone or in combination against ureaplasma urealyticum.METHODS Multiple-proportional broth microdilution method for erythromycin and levofoxacin alone and checkerboard titration methods for them in combination were applied to detect the MICs against ureaplasma urealyticum.The results were evaluated with both fractional inhibitory concentration index and Ridit analysis.The resistant concentration for both erythromycin and levofloxacin was set MIC≥8 mg·L-1.RESULTS 51 clinical strains were enrolled in the study.After combination,the MICs of erythromycin-resistant strains were decreased(P0.05) while that of the sensitive strains increased(P0.05),whereas the MICs of levofloxacin either sensitive or resistant strains were decreased(P0.05).Furthermore,the MICs of levofloxacin-resistant strains decreased more evidently than that of sensitive strains.The MICs of erythromycin were raised in the strains which were sensitive to both erythromycin and levofloxacin after combination(P0.05).The antagonistic ratio in the strains resistant to either erythromycin or levofloxacin were fewer than that of sensitive strains,respectively.CONCLUSION The combination of erythromycin and levofloxacin is helpful to decrease the MICs of levofloxacin against ureaplasma urealyticum and that of erythromycin against erythromycin-resistant strains as well.The combination may reverse the resistance of the erythromycin-resistant strains,but may increase the resistance to erythromycin on the erythromycin-sensitive strains.However,the findings may suggest avenues of research into new treatment strategies employing antimicrobial combinations with improved selection against resistance,if possible.