The Effects of Low Concentration Colistin on Pseudomonas aeruginosa Growth

The increased use of colistin (polymyxin E) for the treatment of multi-drug resistant Gram-negative bacterial infections, has created a growing literature investigating the emergence of colistin-resistant bacteria, specifically in Pseudomonas aeruginosa, Acinetobacter baumannii and Klebsiella pneumoniae.[1,2] Colistin has been a ‘last-resort’ antimicrobial peptide for the treatment of multidrug resistant (MDR) Gram-negative bacterial infections, but the increased reports of colistin-resistant bacteria has medical professional looking for combination therapies as a means to treat these MDR bacteria. The reason researchers have focused their attention primarily on combination therapies with colistin is because at high concentrations, colistin has been seen to cause highly toxic and adverse side effects (acute kidney injury, renal failure, etc.). In addition high dosing colistin only creates evolved strains that require a greater minimum inhibitory concentration (MIC) to treat, only adding to the MDR bacteria issue.[3,4] This research is looking to analyze the growth rates of Pseudomonas aeruginosa at low concentrations of colistin to determine whether combinations therapies of specific strains should even be considered given the adverse side effects at high doses (4-8+ mg/L). Combination therapy research has thus far been positive in treating several cases of MDR bacterial infections, this research will assist in isolating several clinical strains of Pseudomonas that may be effective candidates for combination therapy research