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pISSN 2950-9114 eISSN 2950-9122
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Original Article

J Lab Med Qual Assur 2015; 37(4): 209-213

Published online December 31, 2015


Copyright © Korean Association of External Quality Assessment Service.

Discordance in Colistin Susceptibility Test for Acinetobacter baumannii Showing Resistance: MicroScan versus Etest

Goeun Kang, Hyun Soo Kim, Han-Sung Kim, Wonkeun Song, and Jae-Seok Kim

Department of Laboratory Medicine, Hallym University Kangdong Sacred Heart Hospital, Hallym University College of Medicine, Seoul, Korea

Correspondence to:Jae-Seok Kim
Department of Laboratory Medicine, Hallym University Kangdong Sacred Heart Hospital, Hallym University College of Medicine, 150 Seongan-ro, Gangdong-gu, Seoul 05355, Korea
Tel: +82-2-2224-2327 Fax: +82-2-2224-2214 E-mail: jaeseok@hallym.or.kr

Received: September 2, 2015; Revised: October 21, 2015; Accepted: November 3, 2015

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.


Background: Acinetobacter baumannii causes various hospital-acquired infections, its multidrug resistance is rapidly increasing worldwide. Although colistin is used in treatments against multidrug-resistant A. baumannii , resistance to colistin has also been reported recently. Few studies have reported colistin susceptibility testing using MicroScan. In this study, we compared colistin susceptibility tests for resistant A. baumannii by MicroScan (Siemens, USA) and Etest (BioMerieux, France).
Methods: We collected 115 A. baumannii clinical isolates, showing colistin resistance (minimum inhibitory concentration [MIC] ≥4 µg/mL) by MicroScan, from July 2014 to March 2015 at Kangdong Sacred Heart Hospital. Species identification and antimicrobial susceptibility tests were performed using the MicroScan Neg Combo Panel Type 72. Additionally, Etest was also performed for comparison.
Results: Of the 115 isolates, Etest revealed that 103 (89.6%) were colistin-susceptible (MIC ≤I µg/mL). Moreover, 52 isolates, showing a MIC of 4 µg/mL by MicroScan, were all susceptible to colistin. Only 12 (19.0%) of 63 isolates, showing a MIC of >4 µg/mL by MicroScan were resistant to colistin according to the Etest.
Conclusions: The MicroScan automated system, using the commercial broth microdilution method, exhibited some discrepancies with the Etest for colistin susceptibility in A. baumannii. Therefore, more practical and reliable susceptibility tests for colistin are required in clinical laboratories using MicroScan.

Keywords: Acinetobacter baumannii , Colistin, Microbial sensitivity tests, MicroScan, Etest


  1. Cai Y, Chai D, Wang R, Liang B, Bai N. Colistin resistance of Acinetobacter baumannii: clinical reports, mechanisms and antimicrobial strategies. J Antimicrob Chemother 2012;67:1607-15.
    Pubmed CrossRef
  2. Koh EM, Lee SG, Kim CK, Kim M, Yong D, Lee K, et al. Microorganisms isolated from blood cultures and their antimicrobial susceptibility patterns at a university hospital during 1994-2003. Korean J Lab Med 2007;27:26575.
  3. Ko KS, Suh JY, Kwon KT, Jung SI, Park KH, Kang CI, et al. High rates of resistance to colistin and polymyxin B in subgroups of Acinetobacter baumannii isolates from Korea. J Antimicrob Chemother 2007;60:1163-7.
    Pubmed CrossRef
  4. Park YK, Peck KR, Cheong HS, Chung DR, Song JH, Ko KS. Extreme drug resistance in Acinetobacter baumannii infections in intensive care units, South Korea. Emerg Infect Dis 2009;15:1325-7.
    KoreaMed CrossRef
  5. Manchanda V, Sanchaita S, Singh N. Multidrug resistant acinetobacter. J Glob Infect Dis 2010;2:291-304.
    Pubmed KoreaMed CrossRef
  6. Dafopoulou K, Zarkotou O, Dimitroulia E, Hadjichristodoulou C, Gennimata V, Pournaras S, et al. Comparative Evaluation of Colistin Susceptibility Testing Methods among Carbapenem-Nonsusceptible Klebsiella pneumoniae and Acinetobacter baumannii Clinical Isolates. Antimicrob Agents Chemother 2015;59:4625-30.
    Pubmed CrossRef
  7. Lee SY, Shin JH, Lee K, Joo MY, Park KH, Shin MG, et al. Comparison of the Vitek 2, MicroScan, and Etest methods with the agar dilution method in assessing colistin susceptibility of bloodstream isolates of Acinetobacter species from a Korean university hospital. J Clin Microbiol 2013;51:1924-6.
    Pubmed KoreaMed CrossRef
  8. Lo-Ten-Foe JR, de Smet AM, Diederen BM, Kluytmans JA, van Keulen PH. Comparative evaluation of the VITEK 2, disk diffusion, etest, broth microdilution, and agar dilution susceptibility testing methods for colistin in clinical isolates, including heteroresistant Enterobacter cloacae and Acinetobacter baumannii strains. Antimicrob Agents Chemother 2007;51:3726-30.
    Pubmed KoreaMed CrossRef
  9. Sinirta? M, Akalin H, Gedikoglu S. Investigation of colistin sensitivity via three different methods in Acinetobacter baumannii isolates with multiple antibiotic resistance. Int J Infect Dis 2009;13:e217-20.
    Pubmed CrossRef
  10. Tan TY, Ng SY. Comparison of Etest, Vitek and agar dilution for susceptibility testing of colistin. Clin Microbiol Infect 2007;13:541-4.
    Pubmed CrossRef
  11. Arroyo LA, Garcia-Curiel A, Pachon-Ibanez ME, Llanos AC, Ruiz M, Pachon J, et al. Reliability of the E-test method for detection of colistin resistance in clinical isolates of Acinetobacter baumannii. J Clin Microbiol 2005;43:903-5.
    Pubmed KoreaMed CrossRef
  12. Behera B, Mathur P, Das A, Kapil A, Gupta B, Bhoi S, et al. Evaluation of susceptibility testing methods for polymyxin. Int J Infect Dis 2010;14:e596-601.
    Pubmed CrossRef
  13. Clinical and Laboratory Standards Institute. Performance standards for antimicrobial susceptibility testing. 25th informational supplement, M100-S25. Wayne (PA):Clinical and Laboratory Standards Institute, 2015.
  14. Lee Y, Kim YA, Song W, Lee H, Lee HS, Jang SJ, et al. Recent trends in antimicrobial resistance in intensive care units in Korea. Korean J Nosocomial Infect Control 2014;19:29-36.
  15. Nation RL, Li J. Colistin in the 21st century. Curr Opin Infect Dis 2009;22:535-43.
    Pubmed KoreaMed CrossRef
  16. Albur M, Noel A, Bowker K, Macgowan A. Colistin susceptibility testing: time for a review. J Antimicrob Chemother 2014;69:1432-4.
    Pubmed CrossRef
  17. Humphries RM. Susceptibility testing of the polymyxins:where are we now? Pharmacotherapy 2015;35:22-7.
    Pubmed CrossRef

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