Antimicrobic Vial P Polymyxin B is added to media to improve their selectivity in isolating microorganisms.

• Primarily used for resistant gram-negative infections
• Bactericidal for gram-negative; no impact on gram-positive microbes

Polymyxin B is composed of a number of related compounds. It has a bactericidal action against almost all gram-negative bacilli except the Proteus and Neisseria genera. Polymyxins bind to the cell membrane and alter its structure, making it more permeable. The resulting water uptake leads to cell death.