To add or not to add polysorbate 80: impact on colistin MICs for clinical strains of Enterobacteriaceae and Pseudomonas aeruginosa and quality controls.

Colistin adherence to plastics can be diminished by adding a surfactant, i.e., polysorbate 80. Incorporating polysorbate 80 resulted in 3 twofold and 2 twofold modal MIC decreases for Enterobacteriaceae and Pseudomonas aeruginosa, respectively. The reproducibility of the quality controls (QCs) with and without polysorbate 80 supports the use of Escherichia coli strain 25922 and P. aeruginosa strain 27853.