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J Clin Microbiol. 2019 Mar 28;57(4). pii: e01390-18. doi: 10.1128/JCM.01390-18. Print 2019 Apr.

Antimicrobial Susceptibility Testing for Polymyxins: Challenges, Issues, and Recommendations.

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Laboratory Sciences Research Center, Golestan University of Medical Sciences, Gorgan, Iran.
Department of Microbiology, Faculty of Medicine, Golestan University of Medical Sciences, Gorgan, Iran.
Laboratory Sciences Research Center, Golestan University of Medical Sciences, Gorgan, Iran
Molecular Biology Research Center, System Biology and Poisoning Institute, Baqiyatallah University of Medical Sciences, Tehran, Iran.


Polymyxins, including polymyxin B and polymyxin E (colistin), are now increasingly being used worldwide to treat patients with multidrug-resistant (MDR) Gram-negative bacterial infections. This necessitates that laboratories employ an accurate and reliable method for the routine performance of polymyxin susceptibility testing. A number of reasons have accounted for the difficulties with susceptibility testing for the polymyxins, including their multicomponent composition, poor diffusion in the agar medium, adsorption to microtiter plates, the lack of a reliable susceptibility test, the lack of a specific breakpoint from professional organizations, the synergistic effect of polysorbate 80, and the development of heteroresistance. This minireview discusses such problems that impact the results of currently available susceptibility testing methods. We also provide emerging concepts on mechanisms of polymyxin resistance, including chromosomally and plasmid-mediated mcr-related resistance. Broad-range investigations on such critical issues in relation to polymyxins can be beneficial for the implementation of effective treatment against MDR Gram-negative bacterial infections.


Gram-negative bacteria; antimicrobial susceptibility; colistin; polymyxin resistance

[Available on 2019-09-28]

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