Polymyxin B1 has antimicrobial activity that againsts Pseudomonas aeruginosa ATCC 27853, Acinetobacter baumannii ATCC BAA 747, Klebsiella pneumoniae ATCC 13883, P. aeruginosa 9019, A. baumannii 1261 and K. pneumoniae VM9 isolates with MIC values of 4 μg/mL, 2 μg/mL, 2 μg/mL, 4 μg/mL, 4 μg/mL and 2 μg/mL, respectively.
Polymyxin B1 strongly inhibits protein synthesis in yeast, and in E. coli and S. aureus.