Use of a surfactant (polysorbate 80) to improve MIC susceptibility testing results for polymyxin B and colistin

Diagn Microbiol Infect Dis. 2012 Dec;74(4):412-4. doi: 10.1016/j.diagmicrobio.2012.08.025. Epub 2012 Oct 25.


Accurate determination of in vitro activity for polymyxin class agents has consistently been a problem due to their physical-chemical characteristics that can be influenced by the constituents of reference and/or standardized susceptibility testing methods. We evaluated the impact of using polysorbate 80 (P-80), a surfactant, in reference broth microdilution (BMD) methods when testing polymyxin B and colistin against 247 clinical strains of Enterobacteriaceae (124 strains), Acinetobacter spp. (60 strains), and Pseudomonas aeruginosa (63 strains). All testing was performed in frozen-form BMD panels with and without 0.002% P-80. MIC results for both polymyxins were generally 4- to 8-fold lower when P-80 was added to the testing broth compared to Mueller-Hinton broth without the surfactant. Decreases were greatest in organisms having MIC values at ≤2 μg/mL and among Acinetobacter spp. Polymyxins should be tested with P-80 to more accurately assess the potencies of these agents necessary to treat multidrug-resistant Gram-negative bacilli.

Publication types

  • Evaluation Study

MeSH terms

  • Acinetobacter / drug effects
  • Anti-Bacterial Agents / pharmacology*
  • Colistin / pharmacology*
  • Culture Media / chemistry*
  • Enterobacteriaceae / drug effects
  • Humans
  • Microbial Sensitivity Tests / methods
  • Polymyxin B / pharmacology*
  • Polysorbates*
  • Pseudomonas aeruginosa / drug effects
  • Surface-Active Agents*


  • Anti-Bacterial Agents
  • Culture Media
  • Polysorbates
  • Surface-Active Agents
  • Polymyxin B
  • Colistin