Mupirocin Concentration






0.05 μg/ml


Cells treated with pseudomonic acid within the MIC range, once transferred to fresh media, will spontaneously recover after several hours, and that higher concentrations are necessary for a bactericidal effect.



MIC, ≤0.5 μg/ml


Nearly all clinical isolates of Staphylococcus aureus and Staphylococcus epidermidis, including multiply resistant strains, were susceptible (Mupirocin MIC, ≤0.5 μg/ml) …and the activity of Mupirocin was not greatly influenced by inoculum size, but was significantly enhanced in acid medium.”

Minimum bactericidal concentrations were 8- to 32-fold higher than MICs, and the antibiotic demonstrated a slow bactericidal action in time-kill tests, resulting in 90 to 99% killing after 24 hrs. incubatedat 37˚C.



1 μg/ml at 120 hours


Before the 120-hour mark, regrowth of surviving colonies would occur at 0.25 μg/ml without the presence of mutants, in an inoculum of 106 CFU.

With higher inoculums of 109 CFU, resistant variables (on agar) were found at 2 μg/ml that had stable MICs at 1 - 4 μg/ml Mupirocin, as compared to 0.03 - 0.06 μg/ml for the original inoculum.

Colonies also showed “striking orange/yellow” pigmentation, which was then lost on sub-culture, most likely due to the extra production of β-carotene.

Casewell concluded that this level of resistance “may not be significant” as the topical 2% formulation of Mupirocin contains 20,000 μg/ml of the antibiotic.