Varying linezolid susceptibility of vancomycin-resistant Enterococcus faecium isolates during therapy: a case report

OBJECTIVES: Linezolid is an oxazolidinone antibiotic used in the treatment of infections caused by vancomycin-resistant enterococci. Resistance to linezolid has been associated with a G2576U mutation in domain V of the 23S rRNA. Patient and methods: We present clinical details and susceptibility data from multiple Enterococcus faecium strains isolated from a liver transplant patient over 13 months. MICs of linezolid, vancomycin and quinupristin/dalfopristin were determined using Etest. Molecular typing was performed by pulsed-field gel electrophoresis. Domain V of the 23S rRNA gene in the vancomycin-resistant Enterococcus faecium was amplified. Linezolid concentrations were analysed by HPLC. RESULTS: We report the emergence of resistance to linezolid in a vancomycin-resistant Enterococcus faecium during linezolid treatment. After discontinuation of the linezolid therapy, the isolate reverted to susceptibility. However, after re-administration of linezolid the vancomycin-resistant Enterococcus faecium became resistant to linezolid again. The isolates that were resistant to linezolid had a G2576T mutation in their 23S rDNA. CONCLUSION: We describe a clinical case that shows the shift of a vancomycin-resistant Enterococcus faecium from linezolid resistance to susceptibility and then back to resistance again related to linezolid therapy.