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Clin Infect Dis. 2010 Mar 15;50(6):821-5. doi: 10.1086/650574.

Resistance to linezolid is mediated by the cfr gene in the first report of an outbreak of linezolid-resistant Staphylococcus aureus.

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  • 1Clinical Microbiology Service, Hospital Clínico San Carlos, Madrid, Spain. gmorales.hcsc@salud.madrid.org

Abstract

BACKGROUND:

From April through June 2008, we identified 12 patients in the intensive care unit and 3 patients on other wards infected with methicillin-resistant Staphylococcus aureus that was also resistant to linezolid. We investigated the mechanism of resistance--point mutations in domain V of 23S ribosomal RNA (rRNA) or presence of the cfr gene--involved in the outbreak.

METHODS:

Strains for the study were obtained in the intensive care unit and other wards. Minimal inhibitory concentrations were determined using automated methods, the E-test, or dilution in Mueller-Hinton agar in accordance with Clinical and Laboratory Standards Institute guidelines. Strains were genotyped using pulsed-field gel electrophoresis and were sequenced to determine the presence of point mutations in 23S rRNA. The presence of the cfr gene was determined by specific polymerase chain reaction.

RESULTS:

The minimal inhibitory concentrations of linezolid ranged from 16 mg/L to 32 mg/L, and all the strains were susceptible to tigecycline, vancomycin, and daptomycin. Typing of strains sequentially isolated by pulsed-field gel electrophoresis showed that each patient carried only 1 clonal type of linezolid-resistant, methicillin-resistant S. aureus as detected by sequential isolations. The presence of the cfr gene was confirmed in all the isolates. Furthermore, sequencing of domain V of 23S rRNA showed that the most common mechanism of linezolid resistance reported to date, mutation G2576T, was not detected in any of the strains analyzed.

CONCLUSIONS:

We report the presence of the cfr gene underlying the resistance mechanism involved in a clinical outbreak of linezolid-resistant S. aureus.

PMID:
20144045
[PubMed - indexed for MEDLINE]
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