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| Development of Quantitative Reference Material of Enterobacter Cloacae |
| CHEN Min-fan1,FU Bo-qiang1,LIN Jing2,ZHANG Ling1,SUI Zhi-wei1,WANG Jing1 |
1. National Institute of Metrology, Beijing 100029, China;
2. Nanjing Institute of Measurement and Testing Technology, Nanjing, Jiangsu 210049, China |
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Abstract A reference material in globular shape for the quantification of enterobacter cloacae was prepared by vacuum freeze drying and filter method. The viable count of enterobacter cloacae per sphere was measured in cfu value by filter membrane method. After optimizing the protective agent and freeze-drying process parameters, the average survival rate reached 51%. The reference material has uniform shape, smooth appearance and good reconstituability. The homogeneity and stability of the enterobacter cloacae reference material were determined by plate counting method on violet red bile agar (VRBA) culture media. The results showed that the reference material is homogeneous and stable for up to 6 months when stored at -80 ℃. The reference material was characterized by six laboratories with filter membrane method on Endo Agar. The value of the reference material is（2.0±0.1）log10 (cfu/vial), with the relative expanded uncertainty of 10 %(k=2). The content of viable count of enterobacter cloacae in the reference material is 102 cfu /vial, it can be dissolved directly, without dilution and easy to use, and this can reduce the sources of measurement uncertainty.
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Received: 24 March 2017
Published: 11 August 2017
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2017, Vol. 38 
