The influencing factors and methodological evaluation on tigecycline susceptibility testing methods for Acinetobacter baumannii and Klebsiella pneumoniae / 中华检验医学杂志

ABSTRACT

Objective To investigate the factors affecting the susceptibility of tigecycline and assess the testing methods.Methods The 116 isolates of Acinetobacter baumanaii and Klebsiella pneumoniae were collected in 13 hospitals from January to December,2010,to evaluate the effects on the tigecycline susceptibility of the overnight medium,medium brand and lot number,respectively.The 56 isolates of Acinetobacter baumannii and the 47 isolates of Klebsiella pneumoniae were selected randomly according to the MIC distribution proportion in 2010 and 2012.The broth microdilution was taken as the reference method to evaluate the effects of the agar dilution,disk diffusion,MIC Test Strip (MTS) and Vitek2 (GN16) on the susceptibility of tigecycline.Results The essential agreement (EA) of Acinetobacter baumannii and Klebsiella pneumoniae is 89.7％ (52/58)and 87.9％ (51/58) using overnight medium and fresh medium respectively.Both EA and categorical agreement (CA) of the different brands (BBL and Oxoid) and lot numbers are 100％ using agar dilution.According to the FDA break point criteria,the CA/EA is 77.7％ (80/103)/99.0％ (102/103),87.4％ (90/103)/98.1％ (101/103),64.1％ (66/103)/76.7％ (79/103) using agar dilution,MTS,Vitek (GN16) with respect to broth microdilution.The CA is 79.6％ (82/ 103,S≥14 mm,R≤10 mm),69.9％ (72/103,S≥ 16 mm,R≤ 12 mm),34.0％ (35/103,S≥19 mm,R≤14 mm)using disk diffusion method compared with broth microdilution (FDA break point criteria).Conclusions The susceptibility of tigecycline must be tested using fresh medium.The medium brands and lot numbers used in this test have no effects on the tigecycline susceptibility to Acinetobacter baumannii and Klebsiella pneumoniae.There exist the better correlations on MIC using agar dilution and MTS than the disk diffusion and Vitek(GN16) compared with broth microdilution.It is expected that the consistency can be improved by adjusting the break point of disk diffusion.