Comparison of Three Methods in Vitro Susceptibility Test of Tigecycline Against Acinetobacter baumannii

Abstract:

To evaluate different tigecyclin susceptibility testing methods for Acinetobacter baumannii. A total of 119 clinical A.baumannii isolates were collected and tigecycline susceptibilities were tested by the broth microdilution，agar dilution and disk diffusion. The results of three test methods were compared. The MIC50 and MIC90 values obtained by broth microdilution method were 0.5 μg/mL，1 μg/mL respectively，the（FDA/EUCAST breakpoint） susceptible rates were 100%（119/119）/95.0%（113/119），intermediate rates were 0.0%（0/119）/5.0%（6/119）and resistant rates were 0.0%（0/119）/0.0%（0/119）. The MIC50 and MIC90 values obtained by agar dilution method were 2 μg/mL，4 μg/mL respectively，the（FDA/EUCAST breakpoint） susceptible rates were 54.7%（65/119）/33.6%（40/119），intermediate rates were 33.6%（40/119）/21.0%（25/119）and resistant rates were 11.7%（14/119）/45.4%（54/119）.The disk diffusion method（FDA/EUCAST breakpoint）resistant rates were 4.2%（5/119）/36.2%（43/119），intermediate rates were 48.74%（58/119）/31.9%（38/119）and susceptible rates were 47.1%（56/119）/31.9%（38/119）. There were significant differences on susceptible rates among broth microdilution（BDM），agar dilution（ADM） and disk diffusion. As broth microdilution method was reference method，the total error rates of agar dilution method were 41.2%~60.5% and the total error rates of disk diffusion were 47.9%~63.9%.