title: In Vitro Activity of Retapamulin and Antimicrobial Susceptibility Patterns in a Longitudinal Collection of Methicillin-Resistant Staphylococcus aureus Isolates from a Veterans Affairs Medical Center.
abstract: Mupirocin is a topical antimicrobial used to decolonize patients who carry methicillin-resistant Staphylococcus aureus (MRSA), and the topical agent retapamulin may be a potential alternative therapy. The goal of this study was to determine the in vitro activity of retapamulin as well as a panel of 15 antimicrobial agents, including mupirocin, for 403 MRSA isolates collected longitudinally from a naive population at the Veterans Affairs Puget Sound Health Care System. The MICs for retapamulin had a unimodal distribution, ranging from 0.008 to 0.5 μg/ml. One isolate had an MIC of >16 μg/ml, was also resistant to clindamycin and erythromycin, and was recovered from the nares of a patient undergoing hemodialysis. Twenty-four isolates (6%) and 11 isolates (3%) demonstrated low-level resistance (MICs of 8 to 64 μg/ml) and high-level resistance (MICs of ≥ 512 μg/ml), respectively, to mupirocin. Isolates were recovered from 10 patients both before and after mupirocin therapy. Of those, isolates from 2 patients demonstrated MIC changes postmupirocin therapy; in both cases, however, strain typing demonstrated that the pre- and postmupirocin strains were different. A total of 386 isolates (96%) had vancomycin MICs of ≤ 1.0 μg/ml; 340 isolates (84%) were resistant to levofloxacin, 18 isolates (4.5%) were resistant to trimethoprim-sulfamethoxazole, and 135 isolates (33%) had elevated MICs of 4 μg/ml for linezolid. The baseline levels of resistance were low for mupirocin (9%) and even lower for retapamulin (0.25%) Although the use of mupirocin is currently the standard therapy for decolonization practices, the activity of retapamulin warrants its consideration as an alternative therapy in MRSA decolonization regimens.
authors.affiliation: VA Puget Sound Health Care System, Seattle, Washington, USA University of Washington, Seattle, Washington, USA harria@uic.edu.
authors.forename: Amanda T
authors.initials: AT
authors.lastname: Harrington
authors.affiliation: University of Washington, Seattle, Washington, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Black
authors.affiliation: VA Puget Sound Health Care System, Seattle, Washington, USA University of Washington, Seattle, Washington, USA.
authors.forename: Jill E
authors.initials: JE
authors.lastname: Clarridge
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics*; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics*; D019086:Bridged Bicyclo Compounds, Heterocyclic / Q000494:pharmacology*; D004224:Diterpenes; D006801:Humans; D000069349:Linezolid / Q000494:pharmacology; D008137:Longitudinal Studies; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D016712:Mupirocin / Q000494:pharmacology; D013203:Staphylococcal Infections / Q000382:microbiology; D014481:United States; D014728:Veterans
chemical_list: D018528:ATP-Binding Cassette Transporters; D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D019086:Bridged Bicyclo Compounds, Heterocyclic; D004224:Diterpenes; C000612285:vgaA protein, Staphylococcus aureus; C508887:retapamulin; D016712:Mupirocin; D000069349:Linezolid