Mupirocin (trade names Bactroban, Centany) is an antibiotic. It is used topically and is effective against Gram-positive bacteria, including MRSA. Mupirocin is inactive for most anaerobic bacteria, mycobacteria, mycoplasma, chlamydia, yeast and fungi. Mupirocin is bacteriostatic at low concentrations and bactericidal at high concentrations. It is of the monoxycarbolic acid class. Mupirocin is a mixture of several pseudomonic acids, with pseudomonic acid A (PA-A) constituting greater than 90% of the mixture. Also present in mupirocin are pseudomonic acid B with an additional hydroxyl group at C8, pseudomonic acid C with a double bond between C10 and C11, instead of the epoxide of PA-A, and pseudomonic acid D with a double bond at C4` and C5` in the 9-hydroxy-nonanoic acid portion of mupirocin. It is on the World Health Organization's List of Essential Medicines, the most important medications needed in a basic health system. It was originally isolated from Pseudomonas fluorescens, developed by Beecham.