Evaluation of Commercial Products for Colistin and Polymyxin B Susceptibility Testing for mcr-Positive and Negative Escherichia coli and Klebsiella pneumoniae in China

Qi Zhang,1,* Wenjuan Yan,1,* Yingjie Zhu,2,* Nan Jing,1 Shanmei Wang,1 Youhua Yuan,1 Bing Ma,1 Junhong Xu,1 Yafei Chu,1 Jiangfeng Zhang,1 Qiong Ma,1 Baoya Wang,1 Wenbo Xu,1 Liqiang Zhu,3 Ying Sun,2 Caiqin Shi,4 Juan Fang,5 Yi Li,1 Shengqun Liu6 1Department of Clinical Microbiology, Henan Provincial People’s Hospital, People’s Hospital of Zhengzhou University, and People’s Hospital of Henan University, Zhengzhou, People’s Republic of China; 2Department of Clinical Microbiology, Henan No.3 Provincial People’s Hospital, Zhengzhou, People’s Republic of China; 3Department of Clinical Microbiology, The Second Affiliated Hospital of Zhengzhou University, Zhengzhou, People’s Republic of China; 4Department of Microbiology Laboratory, KingMed Diagnostics Group Co., Ltd, Zhengzhou, People’s Republic of China; 5Department of Research and Development, Autobio Diagnostics Co., Ltd, Zhengzhou, People’s Republic of China; 6Department of Anesthesia and Perioperative Medicine, Henan Provincial People’s Hospital, People’s Hospital of Zhengzhou University, and People’s Hospital of Henan University, Zhengzhou, People’s Republic of China*These authors contributed equally to this workCorrespondence: Yi Li; Shengqun Liu, Department of Anesthesia and Perioperative Medicine, Henan Provincial People’s Hospital, People’s Hospital of Zhengzhou University, and People’s Hospital of Henan University, Weiwu Road 7, Zhengzhou, Henan, 450003, People’s Republic of China, Tel +8613526882118, Fax +8637187160318, Email liyilabmed@henu.edu.cn; tim2002627@163.comPurpose: To evaluate the performance of five widespread commercial products for colistin and polymyxin B susceptibility testing in China for mcr-positive and -negative Escherichia coli and Klebsiella pneumoniae.Methods: A total of 132 E. coli and 83 K. pneumoniae strains (including 68 mcr-1-positive E. coli and 28 mcr-8-positive K. pneumoniae) were collected. We analysed the performance of colistin susceptibility (with Vitek 2 and Phoenix M50) and the performance of polymyxin B susceptibility (with DL-96II, MA120, and a Polymyxin B Susceptibility Test strip; POL E-strip). Broth microdilution was used as the gold standard. Categorical agreement (CA), essential agreement (EA), major error (ME), and very major error (VME) were calculated for comparisons.Results: For E. coli, the total CA, EA, ME, and VME to colistin were as follows: Vitek 2, 98.5%/98.5%/0%/2.9%; and Phoenix M50, 98.5%/97.7%/0%/2.9%. The total CA, EA, ME, and VME to polymyxin B were as follows: POL E-strip, 99.2%/63.6%/1.6%/0%; MA120, 70.0%/-/0%/58.8%; and DL-96II, 80.2%/-/1.6%/36.8%. Only Vitek 2 and Phoenix M50 presented satisfactory performances for mcr-1-positive E. coli. For K. pneumoniae, the total CA, EA, ME, and VME to colistin were as follows: Vitek 2, 73.2%/72.0%/0%/61.6%; and Phoenix M50, 74.7%/74.7%/0%/58.3%. The total CA, EA, ME, and VME to polymyxin B were as follows: POL E-strip, 91.6%/74.7%/2.1%/16.7%; MA120, 92.8%/-/2.1%/13.9%; and DL-96II, 92.2%/-/2.1%/8.3%. All systems were unsatisfactory for mcr-8-positive K. pneumoniae. When the susceptibility of mcr-negative strains was tested, all systems presented excellent performance.Conclusion: Vitek 2 and Phoenix M50 with colistin for E. coli showed acceptable performance regardless of mcr-1 expression, while DL-96II, MA120, and the POL E-strip performed worse for mcr-1-positive strains. Furthermore, mcr-8 greatly affected the performance of all systems with both colistin and polymyxin B for K. pneumoniae isolates.Keywords: polymyxin B, colistin, mobilised colistin resistance, broth microdilution, susceptibility testing, semi-automated systems