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

Area of Science:

• Microbiology
• Infectious Diseases
• Pharmacology

Background:

• Polymyxin antibiotics (polymyxin B and colistin) are vital for treating multidrug-resistant Gram-negative infections.
• Accurate in vitro susceptibility testing of polymyxins is challenging due to their physicochemical properties.
• Standardized testing methods can be influenced by formulation components, affecting drug potency determination.

Purpose of the Study:

• To evaluate the impact of polysorbate 80 (P-80) on the in vitro activity of polymyxin B and colistin.
• To assess the influence of P-80 on minimum inhibitory concentration (MIC) determination using broth microdilution (BMD).
• To determine if P-80 inclusion improves polymyxin potency assessment against key Gram-negative pathogens.

Main Methods:

• Tested polymyxin B and colistin against 247 clinical isolates of Enterobacteriaceae, Acinetobacter spp., and Pseudomonas aeruginosa.
• Utilized frozen-form broth microdilution (BMD) panels with and without 0.002% polysorbate 80 (P-80).
• Compared MIC results obtained with and without the addition of P-80 in the testing medium.

Main Results:

• MIC values for both polymyxins were consistently 4- to 8-fold lower when P-80 was included in the broth.
• The observed reduction in MICs was most pronounced for organisms with baseline MICs ≤2 μg/mL.
• Acinetobacter spp. showed the greatest decrease in polymyxin MICs with the addition of P-80.
• Polymyxin susceptibility testing demonstrated improved accuracy with P-80 addition.

Conclusions:

• Polysorbate 80 (P-80) inclusion in broth microdilution methods significantly enhances the accurate determination of polymyxin B and colistin in vitro activity.
• Testing polymyxins with P-80 is crucial for correctly assessing their potency against challenging Gram-negative pathogens.
• Optimized susceptibility testing methods are essential for guiding the effective treatment of infections caused by multidrug-resistant Gram-negative bacteria.