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In vitro activity of retapamulin against Staphylococcus aureus isolates resistant to fusidic acid and mupirocin

Abstract number: P589

Woodford N., Afzal-Shah M., Warner M., Livermore D.

Objectives: Retapamulin is a novel pleuromutilin antibiotic licensed in the USA in 2007 for the topical treatment of impetigo caused by S. aureus and Streptococcus pyogenes; It is also licensed in Europe for treatment of impetigo and secondarily infected open wounds caused by the same organisms. We determined its activity in vitro against current S. aureus isolates from the UK, including many resistant to fusidic acid and/or highly resistant to mupirocin.

Methods: Six-hundred and sixty four isolates of S. aureus were recovered from storage. These had been submitted for reference investigation from laboratories throughout the United Kingdom. MICs were determined on Mueller-Hinton agar in accordance with CLSI guidelines. Susceptibility was categorised using CLSI criteria, where available; otherwise BSAC criteria were used (for mupirocin and fusidic acid).

Results: Susceptibilities of the 664 isolates are summarised below:

The S. aureus included 488 (74%) MRSA (oxacillin MICs >2 mg/L), 336 isolates (51%) resistant to fusidic acid (MICs >1 mg/L), and 254 (38%) with high-level mupirocin resistance (MICs >256 mg/L); 103 (16%) isolates were resistant to both to fusidic acid and to high levels of mupirocin. Retapamulin inhibited 663 (99.9%) isolates at leqslant R: less-than-or-eq, slant0.25 mg/L; a single MRSA isolate, also with high level mupirocin resistance required a retapamulin MIC of 2 mg/L.

Conclusions: As a reflection of its unique mode of action, retapamulin has demonstrated excellent activity in vitro vs. S. aureus, irrespective of their level of resistance to other antibacterials.

Session Details

Date: 19/04/2008
Time: 00:00-00:00
Session name: 18th European Congress of Clinical Microbiology and Infectious Diseases
Subject:
Location: Barcelona, Spain
Presentation type:
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