Mupirocin is an RNA synthetase inhibitor antibacterial produced by fermentation using the organism Pseudomonas fluorescens.
Mechanism of Action
Mupirocin inhibits bacterial protein synthesis by reversibly and specifically binding to bacterial isoleucyl-transfer RNA (tRNA) synthetase.
Mupirocin is bactericidal at concentrations achieved by topical administration. Mupirocin is highly protein bound (greater than 97%) and the effect of wound secretions on the minimum inhibitory concentrations (MICs) of mupirocin has not been determined.
Resistance
When mupirocin resistance occurs, it results from the production of a modified isoleucyl-tRNA synthetase, or the acquisition of, by genetic transfer, a plasmid mediating a new isoleucyl-tRNA synthetase. High-level plasmid-mediated resistance (MIC ≥512 mcg/mL) has been reported in increasing numbers of isolates of S. aureus and with higher frequency in coagulase-negative staphylococci. Mupirocin resistance occurs with greater frequency in methicillin-resistant than methicillin-susceptible staphylococci.
Cross Resistance
Due to its mode of action, mupirocin does not demonstrate cross resistance with other classes of antimicrobial agents.
Antimicrobial Activity
Mupirocin has been shown to be active against susceptible isolates of S. aureus and S. pyogenes, both in vitro and in clinical trials [see Indications and Usage (1)]. The following in vitro data are available, but their clinical significance is unknown. Mupirocin is active against most isolates of Staphylococcus epidermidis.
Susceptibility Test Methods
High-level mupirocin resistance (≥512 mcg/mL) may be determined using standard disk diffusion or broth microdilution tests.1,2 Because of the occurrence of mupirocin resistance in methicillin-resistant S. aureus (MRSA), it is appropriate to test MRSA populations for mupirocin susceptibility prior to the use of mupirocin using a standardized method.3,4,5