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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].

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