Colistin and Polymyxin B Minimal Inhibitory Concentrations Determined by Etest Found Unreliable for Gram-Negative Bacilli

摘要

Background:A reliable method of polymyxin B and E (colistin) susceptibility testing remains elusive. These drugs diffuse poorly into agar, creating potentially inaccurate Etest and disk diffusion results, and testing by these methods is not recommended. Broth microdilution is the reference testing method, although it can be sometimes difficult to interpret. Currently, when a colistin susceptibility test is ordered for a patient in the Ochsner Health System, our diagnostic microbiology laboratory performs the Etest. As an in-house quality assessment project, we compared colistin and polymyxin B minimal inhibitory concentrations (MICs) determined by Etest with MICs determined by broth microdilution to evaluate whether colistin MICs are accurately being reported by Etest.