title: Use of a surfactant (polysorbate 80) to improve MIC susceptibility testing results for polymyxin B and colistin.
abstract: 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.
authors.affiliation: JMI Laboratories, North Liberty, IA, USA.
authors.forename: Helio S
authors.initials: HS
authors.lastname: Sader
authors.forename: Paul R
authors.initials: PR
authors.lastname: Rhomberg
authors.forename: Robert K
authors.initials: RK
authors.lastname: Flamm
authors.forename: Ronald N
authors.initials: RN
authors.lastname: Jones
mesh_terms: D000150:Acinetobacter / Q000187:drug effects; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D003091:Colistin / Q000494:pharmacology*; D003470:Culture Media / Q000737:chemistry*; D004755:Enterobacteriaceae / Q000187:drug effects; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods; D011112:Polymyxin B / Q000494:pharmacology*; D011136:Polysorbates; D011550:Pseudomonas aeruginosa / Q000187:drug effects; D013501:Surface-Active Agents
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D011136:Polysorbates; D013501:Surface-Active Agents; D011112:Polymyxin B; D003091:Colistin