Polymyxin B, a mixture of polymyxins B1 and B2, is obtained from Bacillus polymyxa strains. Polymyxin B exhibits bactericidal activity against major multidrug-resistant gram-negative bacteria, most fungi and gram-positive bacteria. As basic polypeptides of about eight amino acids, polymyxins B1 and B2 have cationic detergent action on cell membranes. Moreover, polymyxin B is used for infections with gram-negative organisms, which may be nephrotoxic and neurotoxic. Polymyxin B is appropriate to treat the infections of the meninges, urinary tract, and blood stream, triggered by susceptible Pseudomonas aeruginosa strains.

In vitro: Polymyxin B elicited up-regulation of dendritic cells (DCs) maturation markers, including the increase in the in the expression of co-stimulatory molecule CD86 and HLA-class I and II molecules. Polymyxin B induced a progressive increase in the adhesion property of human DCs. In addition, polymyxin B triggered the activation of the ERK1/2 pathway and IκB-α/NF-κB pathways [1].

In vivo: Male bacteraemia ddY mice were subcutaneously treated with polymyxin B at a dose of 5, 10, 15 or 20 mg/kg for 7 days. Polymyxin B, in a dose-dependent fashion, improved the survival both of OU-01062- and OU-98039-infected mice. In polymyxin B-treated mice, except for 5 mg/kg polymyxin B, the viable cell counts had a tendency to reduce steadily in each concentration group. It was showed a rapid and marked decline of bacterial cell count between 3 to 6 h after infection [2].

References:
[1].  Valentinis, B., Bianchi, A., Zhou, D., Cipponi, A., Catalanotti, F., Russo, V., & Traversari, C. Direct Effects of Polymyxin B on Human Dendritic Cells Maturation: THE ROLE OF I B- /NF- B AND ERK1/2 PATHWAYS AND ADHESION. Journal of Biological Chemistry. 2005; 280(14): 14264-14271.
[2].  Miyajima, Y., Hiramatsu, K., Mizukami, E., Morinaga, R., Ishii, H., & Shirai, R. et al. In vitro and in vivo potency of polymyxin B against IMP-type metallo-β-lactamase-producing Pseudomonas aeruginosa. International Journal of Antimicrobial Agents. 2008; 32(5): 437-440.