Abstract：Objective To evaluate different in vitro tigecycline susceptibility test methods for carbapenem-resistant Klebsiella pneumoniae (CRKP). To understand the resistance of CRKP to tigecycline in Liaoning province, and provide evidence for rational clinical drug use. Methods A retrospective collection of 269 strains of CRKP isolated from January 2011 to December 2016 in several large hospitals in Liaoning province. Sensitivity of tigecycline to CRKP was detected by the broth microdilution method (BMD), the K-B disk diffusion method, the Vitek-2 method, and the E-test method. Results The MIC50 and MIC90 of BMD, the E-test method, and the Vitek-2 method were as follows: (0.5/1), (0.25/0.5) and (0.5/4)μg/mL. According to the US Food and Drug Administration (FDA) and the European Committee on Antimicrobial Susceptibility Testing (EUCAST), the sensitivity of CRKP to tigecycline by BMD was 97.4%/93.3%, and the intermediate rate was 2.2%/4.1%, and the resistance rate was 0.4%/2.6%. The E-test method had the highest sensitivity rate of 100%/98.9%, the Vitek-2 had the highest resistance rate of 8.6%/13.4%, and the disk diffusion method had the highest intermediate rate of 11.9%/46.5%. Compared with the BMD method, the essential agreement rates (EA) and the categorical agreement rates (CA) of the E-test method were≥90%, but there was the very major error (VME) of 0.4%/1.9%, respectively. In the Vitek-2 results, EA was only 61.7%, CA was 87.4%/72.1%, the major error (ME) was 6.3%/7.4%，and no VME was produced. The results using the disk diffusion method, CA was only 85.9%/46.5%, the minor error (mE) was 1.9%/2.6%, and the ME was 0.7%/5.6%. A total of 251 CRKP tigecycline MIC<2μg/mL was determined by the BMD method. Most of the MIC values measured by the E-test method were the same as or different from the BMD method by ±1 dilution. The MIC values measured by the Vitek-2 method were higher than those of the BMD method. 1, 2, and 3 dilutions accounted for 40.2%, 27.5% and 10.4%, respectively. Conclusion The vast majority of CRKP in Liaoning still maintains high sensitivity to tigecycline. For CRKP, the E-test method, the Vitek-2 method, and the disk diffusion method are not suitable for the detection of tigecycline sensitivity alone. Joint detection can be considered and the BMD method should be referred to when results are inconsistent.
