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Confirmation of high-level mupirocin resistance in S. aureus isolates using the mupA EvigeneTM kit

Abstract number: P594

Skov R.L., Hansen L.

Objectives: Mupirocin is the only anti Staphylococcus aureus topical antibiotic licensed for eradication treatment of nasal carriage of S. aureus. Mupirocin resistance occurs both as "high level" or "low level." Since application of mupirocin ointment into the external nares results in concentrations >20,000 mg/L, only high-level resistance (MIC of >256 mg/L) is significant in this setting. High-level resistance is caused by the expression of the mupA (or ileS-2) gene that encodes an additional isoleucyl tRNA-synthetase that is not bound by mupirocin. In this study we investigated the mupA EvigeneTM kit for confirmation of mupA high-level resistance in isolates screened positive using a 5 mg mupirocin disc.

Material and Methods: A total 39 out of 4692 clinical S. aureus isolates (1223 were MRSA) with an inhibition zone <20 mm against a 5 mg mupirocin disc were investigated. The 39 isolates were tested by mupA EvigeneTM hybridisation assay with capture and detection probes for the mupA gene producing a red colour, assay time of 3.5 hours. Wells were read both visually and using an ELISA reader at 490nm, using an OD of 0.50 as cut off. The isolates were further MIC tested by E-test (using the manufacturer's instructions) and a 200 mg mupirocin disc using confluent inoculum on Mueller Hinton agar. S. aureus ATCC 29213 (mupA negative) and AIS2006–079 (mupA positive) were included in all runs.

Results: Six isolates, all MRSA, were found positive for mupA by the mupA EvigeneTM both visually and using Elisa reader (OD 2.0–2.7 for positive compared to <0.16 for mupA negative isolates). All 6 mupA positive isolates had MIC >1024 mg/L and inhibition zones <13mm using a 200 mu;g disc, whereas mupA negative isolates had MICs between 0.064 and 8 mg/L and inhibition zones between 20 and 37mm by disk diffusion.

Conclusion: In summary, the mupA EvigeneTM identify isolates with high-level resistance to mupirocin fast (3.5 hours) from isolates with low resistance. This investigation supports the use of mupA EvigeneTM in clinical settings for the confirmation of high-level resistance in mupirocin resistant S. aureus.

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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